Not what you think it means, although they may well possess them...
There's something about a person in uniform. It's not just due to Hollywood's inability to cast unattractive people; something about the cut, colors and symbolism of military drag can bump a person up a couple of points on the hotness meter.
For one thing, uniforms are designed to look... well... uniform, so that troops look good en masse. Dress uniforms are deliberately tailored to create a neat-but-athletic look; tactically practical battle uniforms are less pretty, but have their own appeal...yes, even on females.
It's the martial equivalent of She Cleans Up Nicely. Compare Fair Cop, Hot Men At Work, Hello, Sailor, and Firemen Are Hot. While traditionally a result of a Female Gaze, that's rapidly changing.
Keep in mind, this is NOT just "hot actor in a military uniform." There must be an in-story acknowledgement that the person is better looking because of the uniform.
Conversed in Baccano! 1931 - Another Junk Railroad. When Claire goes to Rachel for advice on what to get for Chane, she suggests clothes. Upon hearing this Claire immediately jumps to the conclusion that he should get her military uniform, the suggestion being that he believes anyone automatically looks sexier in a military uniform. Rachel manages to talk him down into getting her a normal dress, but not out of sewing knife-holsters into it.
In Mafalda, Susanita gets excited about Manolito's brother returning from military service... until he tells his brother wasn't a cadet, but a recruit, something which disgusts her.
In Albedo Erma Felna EDF, Erma, furryCat Girl officer, looks great in both her regular duty and flight gear, but put her in her dress uniform, a tight backless single piece of material with slippers and a cape to frame it, and she becomes a knockout who can stun any male.
In Eyes Wide Shut Nicole Kidman makes her husband Tom Cruise jealous when she reveals that she has fantasies about a Naval officer in dress whites she met when their family was on vacation.
Taking Chance: Lampshaded by a girl in the seat next to Lt. Colonel Strobl, texting about the "HOT Soldier" sitting next to her.*
Strobl leans over and corrects her - He's a Marine.
Ted: Lori and John discuss the night they met, with cutscenes showing their very different recollections of the event. Lori remembers John practically knocking her out with his spastic dance moves, while John's version contains choreographed dances, suave one-liners...and he's wearing Navy dress whites for some reason.
Hostile Takeover has Commander Marc Davidoff, Space Marine and Ace Pilot. Though he's heir to one of the largest oligarchies in the galaxy, and as athletic as you would expect from a man of his job description, CC notes he's not really as handsome as her social-climber fiance. It's Davidoff's blunt manner, spiffy uniform and dedication to duty that make him so attractive.
Pride and Prejudice: Some major sub-plots are driven by the arrival of the ___shire militia to Netherfield. Mainly, Kitty and Lydia go bananas trying to flirt with all the officers, and completely lose interest in any man not wearing a red coat.
Wraith Squadron and later novels: The first impression that most people have of the Wraiths' Kell Tainer is that he'd look good on a recruitment poster.
It isn't properly a military uniform, but one book in the Heralds of Valdemar series contains several paragraphs of discussion as to how everyone looks better in the white Heralds' uniforms.
In George Mc Donald Fraser's McAuslan stories, his Author Avatar Lieutenant Dand Mc Neill reflects on the power of the Scottish military uniform to attract women. He notes that not even American Air Force pilots or the U.S. Marines can compete with a man wearing kilt, sporran, and a ritual dagger down his sock-top.
In "The One With The Chicken Pox" episode of Friends, a shore leave visit by Phoebe's submariner old flame gets the group discussing the appeal of a uniform. Inspired, Ross later treats Rachel by getting hold of some Navy whites and attempting the "An Officer and a Gentleman" carry out.
Rory Williams is Adorkable in civvies (or his nurse's scrubs), but totally Badass in any uniform, be it museum security guard, modern combat fatigues or particularly his signature Roman centurion outfit. In "A Christmas Carol", he's dressed as the last one for his honeymoon, so clearly Amy loves it too.
"Invasion of the hot Italians": For the record, Amy was dressed in her kiss-o-gram constable outfit. Obviously, Rory likes that too.
Acknowledged by General O'Neill of all people in Stargate Atlantis, upon learning that the incoming rescue mission is less than officially sanctioned.
O'Neill: So, am I to assume you are not surrounded by heavily-armed SG teams and young, strapping marines?
In the Star Trek: Voyager episode "Nemesis", a girl from the village says that the Defenders, which Chakotay has joined, "glimpse great" in their jungle combat gear. They're actually the villains of the story.
Horatio Hornblower: When Horatio is promoted to Lieutenant and gets his new Navy uniform, he's praised by his tailor (obviously) that it's a great improvement, compared to his Midshipman look. Men aboard the Indefatigable tease him and Archie jokes that there is a complete stranger among them.
Murdoch Mysteries: Not much is said about constables' normal uniforms, but when they play baseball, all the constables look great in their shirts. Drs. Emily Grace and Julia Ogden are especially impressed with Constable George Crabtree and comment that he looks dashing.
Lampshaded and Double Subverted in Patience. None of the female cast are remotely interested in the Dragoons, instead swooning after the poets Bunthorne and Grosvenor, because aestheticism is all the rage. The soldiers wonder why their uniforms are no longer effective at conquering women, and they only start winning the ladies back when they start to dress and act like aesthetic poets. When Grosvenor gives up the aesthetic game, the women who were chasing after him have a sudden change in taste and go back to the soldiers to whom they were originally engaged.
Quite a few web forums out there - there are least two military discussion forums that have dedicated threads on the subject (with only full-clothed pictures generally allowed) and one dedicated blog.
There is a Polish saying, roughly translated: "all girls want uniform-wearing boys". No known female version probably due to the fact that war used to be a man's job.
During Operation Desert Storm, the Today show featured a live interview with a U.S. Air Force Colonel (i.e. someone roughly Katie Couric's age at the time). When they sent it back to Katie and Bryant, Katie said, "Can you put the Colonel back on? Hubba hubba!"
During Gulf War Cher came back from entertaining the troops to announce that America had the cutest armed forces in the world, including the girls!
Serves as Fetish Fuel for a lot of tourists in Israel, as soldiers in uniform are to be seen practically anywhere, both male and female. This picture in particular made quite a lot of noise...
