A crime, usually an international or diplomatic one, has happened. Someone was paid off by a foreign power. And how were they caught? The foreign power was inconsiderate enough to pay them in their own, rather than domestic, currency. Sometimes this can be justified, for example the bribing party may not have much hard foreign money to hand or the bribed party may have intended to flee the country and defect, but often it is not.
Truth in Television in that possessing foreign currency was itself a crime in the USSR and some of its satellite countries, and bringing more than a specified amount albeit usually quite a large one without declaring it and paying excise is unlawful most other places.
Bit of a Undead Horse Trope in that it's much better proof in the past, when rulers coined their own money both Marc Antony and Octavian issued their own currency, for example, although they shared rulership of the Roman Empire at the time.
It's also not uncommon for somebody to have foreign money planted in their possessions to make it look like they did it. Sometimes part of a False Flag Operation. Can overlap with Global Currency Exception.
- In one Blueberry story, he stops a saboteur who was trying to slow down a railroad company. After arresting him they find gold coins of California Republic. This proves to them that the saboteur was hired by their rival railroad company, who uses those coins to pay their workers.
- In 300, Theron is exposed when he is caught with Persian coins. In Real Life, Persian money was made from precious metals, but Spartan money was made from iron; metaphor alert! While there's no clear reason that he would carry them with him, it does make sense since he fully expected the Persians to take over and make other currencies worthless. Real Life Spartan commanders were often bribed, but tended to keep the money in offshore banks... that is, foreign temples.
- Girl in Gold Boots has Critter introduce himself by asking for change for a hundred, then a fifty. Buzz then tries to rob him, inverting the trope. Later on, we learn that said money is actually Nepalese money. But this trope is then played straight when it's discovered that Critter was hiding in Nepal and now here to keep from being drafted for the Vietnam War.
- Chain Reaction. The protagonists have money planted in their homes to make it look like the Chinese government are bribing them.
- Riggs and Murtaugh get on the case of the Afrikaaner villains in Lethal Weapon 2 after foiling an attempted "theft" (read: money laundering) and discovering that the money stolen was gold Krugerrands, which on top of everything else were illegal to import in the US at the time (in response to the apartheid government).
- In Jingo, the apparent assassin of the visiting prince is apparently paid in Klatchian currency. This is in fact because the room was staged to make it look like an obvious frame-up against the Klatchians, so Vimes would think they didn't hire the assassin, because they did in Ankh-Morpork currency, which was exchanged for Klatchian after their patsy was dead.
- In the X-Wing Series, Dr. Edda Gast, a Mad Scientist, is captured by the New Republic and offers her complete cooperation in return for amnesty for her crimes, a new identity, and half-a-million credits in cash. Though she promises not to return to her previous ways, everybody knows she is lying through her teeth and will return to her previous activities as soon as she is released, and the fact that she demands Imperial credits simply reinforces that. However, the Republic honors their bargain, gives her the new identity and the money, and release her onto Coruscant...where she is promptly arrested by the customs agent at the spaceport. Since the New Republic and the Empire are at war, attempting to bring Imperial credits into the New Republic capital qualifies as smuggling, and since she is carrying so much value in Imperial credits, the charge will actually include attempted sedition as well. Nawara Ven, the Twi'lek lawyer from the Republic that Gast had repeatedly insulted throughout their encounters, had repeatedly asked her if she really wanted to take the money in that fashion, and when Gast had refused any other alternative, he stepped back and let her walk into the customs entrance.
- In The Master and Margarita, there was a guy who got arrested because the police found foreign currency in his apartment; he had accepted a bribe from Satan, but in roubles. Woland/Satan then anonymously called the police, who found the currency, now mysteriously American dollars.
- Curiously, in times when the novel took place it wasn't a crime to possess and even trade in a foreign currencynote ; the regulations were tightened much later, basically only after the Stalin's death, so the guy's only real crime was basically accepting a bribe. The police finding it in dollars would only be a minor problem, adding maybe a misdemeanor to his case.
- This came up a number of times in the Belgariad saga by David Eddings. In this case, however, it is not the stamp on the coins that is a giveaway, but the color the Always Chaotic Evil Murgos have access to a virtually bottomless gold-mine, which has iron contamination in it, giving the gold a red tinge. And they are quite free with it... as such, anyone caught with red gold in their pockets has probably been bribed by the Murgos.
- Murgo gold is also supernaturally addictive, which explains both why they're so lavish with it and why possession of it is considered damning evidence rather than merely suspicious by the main characters.
- The good guys take advantage of this at one point: The Imperial Legions desert en masse within sight of the Imperial capital of Tol Honeth. However, they're induced to do so by "red Murgo gold", which Ce'Nedra (the Imperial princess) is casually scattering about the field while talking about how the Murgo soldiers seem to have so much of it, so it must be just lying around for the taking in Cthol Murgos (which is where she wants them to go). The officers try to stop it, but pretty much the entire rank-and-file defect to the princess from her father.
- Rogue's Home by Hilari Bell has a variation. A man the heroes suspect was bribed to leave town is found dead with foreign currency in his pockets. One of the coins is from a faraway town that only one merchant is known to trade in, implicating him as the briber.
- In Cold Copper Tears, Garrett finds several temple-minted coins that identify the Sons of Hammon cult as the bad guys. Not only are these coins clues, but they're also illegal in Karenta, where the cult and its coinage were outlawed by royal decree over a century before. Justified in that the cult's leaders are so brainwashed that they think no mortal agency can stop them, and that the end of the world is imminent so it won't matter if they're exposed.
- In A Feast for Crows, Cersei Lannister discovers one of the jailers who was guarding Tyrion had a gold coin minted by House Tyrell, who were trying to marry their daughter to her son. Since Tyrion had just murdered their father and escaped after being found guilty for killing Cersei's other son, Joffrey, this made her suspect the Tyrells had bribed the jailer to free Tyrion, even though Lord Tyrell wanted Tyrion dead since his daughter could have died at his hands. It's implied that the jailer was actually spymaster Varys, who presumably left the coin there to encourage Cersei's paranoia about the Tyrells.
- Variation: In The Day Watch, Vitaly discovers that his bag is full of dollars and immediately thinks he's up to something illegal.
- Averted at least once in Robert Jordan's The Wheel of Time series. After a man who tried to kill Rand is found to have Tar Valon coins, one of the Asha'man (who is a traitor himself) argues that this is evidence that the Aes Sedai planned it. Cool Old Guy Davram Bashere promptly points out that many men in the area, including Davram himself, have more than a bit of Tar Valon currency.
- Another aversion happens with a riverboat captain who knows too much. His enemies try to silence him by giving him a packet of letters, a generously sized purse, and an address to which the letters need to be delivered. So far, nothing strange. However, when the captain decides on a whim to count the money, he realizes that all the coins are Tar Valon currency. He then becomes suspicious enough to open a letter and, as you might think, the letter contains accusations of him conspiring with the Aes Sedai. Realizing that the combination of the letters and the money would be enough to get him executed when he reaches his destination, the captain simply burns the letters and asks his first mate if he knows anyone at their destination who might be inclined to buy a large quantity of moody silver quickly and discreetly and not shaft him too badly.
- In Babylon 5, Garibaldi is framed for a bombing, and as part of this, a large quantity (somewhere along the line of two years' salary) in Centauri Ducats are planted in his quarters. Since Centauri are one of the few cultures that still mint physical currency, their coin is the currency of choice for dodgy deals in the setting. That Garibaldi actually spends said currency (the Centauri ambassador is a friend of his and helps him out when he's on the run) doesn't help.
- In Adam-12, a soldier at the Los Angeles airport coming home from Japan claims to have been robbed. The alleged pickpocket says it's his money. The cop, looking at it, points out that Japanese Yen spends pretty hard here.
- In the BBC series Sherlock, Sherlock Holmes suspects a car dealer of having lied about traveling overseas. He sneaks a peak in the man's wallet and sees a Colombian banknote, the final clue he needs to solve the case.
- In Castle, a victim is suspected to be a spy involved in something highly questionable when his car is discovered with a large quantity of Euros in the trunk. Subverted the victim was actually on a 'spy vacation' and the Euros were part of the game. And then double subverted; real foreign money was never used in-game the money found in the car was actually more than the price of the spy vacation itself. Eventually it turns out to be a side-scheme by one of the vacation company employees.
- When Phoebe was a Salvation Army bell ringer during the holidays on Friends, she was disillusioned by her customers and was rude back and her corner was taken away. When the new girl came to take over, Phoebe said she would give her one piece of advice: to "watch out for that bitch" (a lady who tried to donate a Canadian coin).
- There was a variation in Journeyman in which an FBI Agent caught on to the fact that Dan Vassar was a time traveller, part of his case being that Vasser was in possession of money from different eras.
- Torchwood: Miracle Day. Esther Drummond gets a phone call from her bank asking how she wants to invest the $50,000 that's just been wired from an account in China. Realising she is being set up, she has to get out of CIA headquarters before she's arrested. She contacts her partner Rex Matheson, who is skeptical until he checks the messages on his mobile and finds a text informing him that twice that amount has been deposited in his own account.
- Farscape. In "Crichton Kicks", newcomer Sikozu is suspected of working with the Scarrans because she has their currency. She points out that everyone else in their gang of outlaws is from Peacekeeper territory, so whose money do they have in their pockets? Her species is under Scarran domination, so naturally they have to use Scarran currency.
- Shadowrun came up with the idea of having the company that hired the shadowrunners pay them in corporate scrip or company stock instead of real money. There are legitimate reasons to do this. However, they apparently didn't consider that if the shadowrunners were caught after being paid, their having the company's scrip or stock would be a dead giveaway that that company was behind the shadowrun.
- That is, assuming the stock is actually from the company that is behind the run, not the one that your real employer wants you to think that it is from, unless...
- For that matter, most forms of hard currency (as opposed to electronic credit or corporate scrip) are illegal in most of the Sixth World, although that doesn't stop people from trading it on the black market.
- In the card game Banana Republic, the objective is to pay off enough electors to become President of Banania. Now, the citizens of the Republic are used to corruption, but they're also very patriotic; if some muckraking journalist discovers that an elector has been paid with evil American dollars, as opposed to nutritious home-grown bananas, the elector will be forced to repudiate the bribe.
- The Clans in BattleTech automatically believe this in the presence of any hard currency. They only issue 'work scrip' within their own individual clans, implied to be digital currency to exchange for goods, and use a kind of basic coinage known as Kerenskys to allow members of their merchant caste to bargain between clans. The presence of any other sort of currency on anyone is by default considered evidence of participating in the illegal black markets and punished severely, because they accept no other reason that a person would have any form of money that can't be spent openly in the Clan economy.
- In one episode of Biker Mice from Mars, Lawrence Limburger once tried to rid himself of the mice by framing them. The final evidence against the officer bribed by Limburger was a huge pile of Plutarkian money found on the officer's possession.
- Justice League Unlimited: When someone hired to kill Aquaman was caught, his payment clued the heroes to the fact the one who hired the hitman was Orm.
- She-Ra: Princess of Power: In one episode, Imp plants Horde coins in Kowl's bed to make it look like Kowl is a Horde spy.
- Harpo Marx was suspected of being a spy when he entered the USSR because he had rubles. But he had simply exchanged his dollars for rubles with another passenger on the train, not knowing that he had to do it through official channels. So in his case domestic money was proof of guilt.
- Actually, USSR had state monopoly on currency exchange, so during darker times possessing foreign currency was a crime in itself. As operations with it (e.g. exchange). The "valuta" as a word creeped into Russian usage first through underground shroffs who were pursued by officials but still had basically a whole populace for a market because Rouble was (and still is, if you look at fluctuations) just not a very reliable currency and, worse yet, government regularry manipulated it on purpose to get into people's pockets. Ironically, some of the "valutchiki" - as this class of criminals was called - actually made it to banker-oligarchs after the fall of USSR.
- Former Irish Taoiseach (Prime Minister) Bertie Ahern made some unusual deposits to his bank account when he was finance minister — he claimed that he received IR£16,500 from friends as a loan, and about GB£8,000 as a whipround (contributions collected from a group of people for a specific purpose) when he was short on money after his separation. But the sum IR£24,838.49 converts exactly to a GB£25,000 lodgment (deposit).
- On another occasion, a IR£28,772.90 lodgment was made, which he claimed represented about GB£30,0000 in cash. But this amount converts exactly to US$45,000. Clearly something odd was going on, but as yet no charges have been laid.
- Though not using foreign money, a man accused of robbing several vending machines paid his bail with quarters, dimes, and nickels.
- This trope collided with Poor Communication Kills during U.S. Special Forces "Robin Sage" exercise in 2002, a month long war game/ final test for graduating Green Berets where several counties of North Carolina become "The People's Republic of Pineland", complete with police and local government participation. During a traffic stop, a participating Lieutenant and Sergeant attempted to bribe Sheriff's deputy Randall Butler with "Pineland Don", the official Monopoly-esque currency of the exercise, not realising that the deputy had not been briefed. This led to an escalating series of events culminating in the Lt. getting a full can of mace to the face and a fatal gunshot wound, and the Sgt. taking two non-fatal shots in the back while attempting to run to cover with his blank-firing machine gun.
- There is an urban legend of an influential Soviet man who made a lot of money illegally and converted it to US dollars. However, thanks to his influence, the KGB couldn't even search his house for evidence. He was about to emigrate to the US, and invited many influential friends to his going-away party, including the American ambassador. After the party, he boarded the plane and left. The KGB search his luggage and find no money. They then search his house and find a large pile of ash. Turns out he had the ambassador witness him burning all his cash and sign an official document that a certain amount of currency was indeed destroyed. All the man had to do was go to the nearest Federal Reserve bank in the States and show them the document to get his money back. (It is US government practice to replace provably destroyed currency.)
- Western currency, especially USD (used as hard currency for Western, i. e. higher quality goods), made normal citizens suspicious in former Eastern Bloc countries because it was illegal and undermined the value of local currencies by being on the black market. However, it was an Open Secret that high-ranking party members traded in dollars.
- Back when travelers checks were issued on Paper in the U.S. (the creation of American Express, Visa and MasterCard prepaid debit cards and near-universal acceptance of them has mostly eliminated paper travelers check in the U.S.) a common scam when the Canadian Dollar was worth US 65c, was to purchase something in a U.S. store and pay with Canadian traveler's checks, because a CAD$20 check was worth about $14, and get the change in U.S. dollars. The checks look almost identical. Today, actually, it wouldn't matter because Canadian money is almost always at or above USD$1 per CAD. Most stores in the U.S. could probably make money, even with the currency conversion charge, to accept Canadian dollars as equal to a U.S. dollar.
- Part of the evidence used to convict former South African Cricket captain Hansie Cronje of a match-fixing scandal was the fact that he was in possession of foreign money. In South Africa, it is illegal to possess foreign money unless one is travelling to or has recently arrived from a foreign country.