Rouge the Bat is pratically the anthromorphic version of this trope for the entire Sonic franchise.
Sonic Adventure 2 was rated 3+/E for everyone, perhaps surprising when you consider that the lyrics of the Wild Canyon stage are basically Intercourse with You. It contains blatant references to Rouge being "sexy" and how Knuckles wants to "get her with his tools" and is "feeling her in mysterious ways". As well as that, Rouge got away with jiggle physics — to the point of Gainaxing at certain points — throughout the game.
The Jiggle Physics of Rouge becomes funnier when you realize that her boobs bounce in time with her ears.
The absolute example of Rouge's radar busting: Within Rouge's textures in Sonic Adventure 2 is a texture that features her mysteriously detailed nethers.◊
Also included in the lyrics to the Wild Canyon stage is the line "they wanna play with my emeralds?", and considering that the phrase 'the family jewels' is often used an a euphemism for... down there... well...
Sonic Riders also contains a blatant reference to her being "sexy" - in the first Riders game, the tricks you do are named, though you have to know the right series of button presses to perform specific ones. One of the tricks Rouge can do while using a Skate-type gear easily just by holding right for long enough after jumping off a ramp? "Sexy Shot." Plus, her default board is called "Temptation."
In the final cutscene in Sonic Heroes, after Metal Overlord has been defeated, Rouge walks past Knuckles while saying she's going to go after someone else's treasure (she had been looking for Eggman's for almost the entire game), and you can guess what two things it looks like he's looking at as her chest passes inches away from his face.
Knuckles: You'd do that, Rouge? Julie-Su: She'd do anything. Rouge: Watch it, pinky.
In Sonic Heroes, Amy blasphemes. Nothing severe ("Holy Cow!" "Oh my God!") but it's something that rating boards in English-speaking countries tend to frown on. And yet, it didn't hurt their rating in the least.
Another Heroes example: before Vector asks Amy a question, Amy assumes that he's asking for a date and that it will have to wait another time. In hindsight, Amy, a 12-year-old girl rejects going out with a 20-year-old Vector.
An ongoing dispute since Sonic Adventure was released in 1999 rages: just what exactly did the singer say at 1 minute into "My Sweet Passion (Theme of Amy Rose)"? Nobody seems to know for sure, but to paraphrase Blades of Glory, it's [probably] provocative. Just listen to the lyrics all the way through. Consensus: "The Sphinx looked so cute, I had to shave it." In a sultry voice. And the song was long enough to be played during Amy's end credits sans lyric-masking dialogue.
It doesn't help that the background music (Awesome Music that it is) wouldn't feel out of place in a porno... and some of the rest of the lyrics are pretty... suggestive. It is about a pre-teen in love, after all.
Sonic Rush has awesome music, but Intercourse with You is rather blatant in "Vela Nova." Especially when taken in account the context it was used (a fight between Sonic and Blaze). The moans, the noises of deep breathing, and the sexy female voice moaning "Let's do it" in the ending? Veeeeery subtle.
The song's title is Portuguese for "new candle", and from there, even with Blaze's pyrokinesis, it's not too hard to interpret that in the context of something like "Sonic's new flame." Make of that what you will.
In Archie's Sonic the Hedgehog comic, Blaze has been having visions about Sonic in her sleep, and seeks him out. They fight, and afterwards, we get the following exchange:
Blaze: You are indeed the one I have sought out. No question. Sonic: You've been looking for me? Who are you exactly? Blaze: The one who will now haunt your dreams the way you have haunted mine! Farewell, Sonic... Until I have need of you! Sonic: (thinking to himself) Haunt my dreams, huh? I wonder...
Sonic Adventure 2's final boss, The FinalHazard. The fact that it's a moaning, writhing beast which shoots lasers from its underside could be unintentional, but where's the Eclipse Cannon pointing?
For a similar version from the Archie Comics verse, we get this little jewel after Tails asks if Antoine n' Bunnie will be bored while he's off at his little workshop.
Antoine: "Will we be bored", he asks.
Bunnie: You hush. He's still a young'un.
If you keep in mind that they're supposed to be on their honeymoon, one doesn't have to guess what they plan to do with their alone time...
An earlier example from the aforementioned Rouge examples: In Archie's Sonic the Hedgehog comic Spin-OffKnuckles the Echidna, one arc is centered around one of Charmy Bee's friends dying of Lemon Sundrop Dandelion poisoning. Take the first letter from each word and what do you get? Subtle, huh?
According to Word of Gay, they were forced to do this to get the Rotor/Cobar relationship through in the "Mobius: X Years Later" Alternate Time Line arc (though, in a subversion, on orders from the parent company to avoid the inevitable Internet Backdraft, than as a deliberate attempt to sneak it past the censors). Just look at these exchanges, and see for yourself:
Rotor: Having confirmed my findings of the entropic effect upon Mobius with Cobar, an Echidna scientist possessing a formidable intellect with whom I enjoy a close personal relationship.
Espio: Well, Rotor wasn't forthcoming, but I suspect he was also here to see Cobar.
Knuckles: That's not surprising — given their history!
Cobar: My dear Rotor, and I say this with affection and respect, but have you gone mad?
There was also a nod at the whole early 90s "Teen Talk Barbie" controversy with a story involving Robotnik building doll-versions of Rabbot and Sally that say phrases like "I belong in the kitchen".
The Wii version of Sonic Colors gives us a nice gem too as Orbot and Cubot pick up pieces of Rotatatron, though it only really falls into this if you think about it.
Cubot: The bossman said to wrangle every piece o' this mess. When you consider what we're doin' from a robot's point of view, it's actually pretty gruesome.
Sonic Adventure 2 actually managed to get away with not only having the government kill everyone aboard the ARK, but also manage to have Gerald Robotnik being executed by firing squad. Sure, they didn't show the actual death, but the fact they clearly implied it in an E-rated game is astonishing.
On the subject of implied death, we have Maria. Like with Gerald, Sonic Team implied that she died instead of blatantly showing it. However, flashbacks about it appear much more frequently than Gerald's death scene in the game. Still, it's surprising how this showed up in a Sonic game, of all things.
The theme for Sonic Adventure 2's stage Death Chamber says, "You're damn right, Knuckles!" note It was censored in the GameCube version by removing the conversation containing the line in question from the song.
Knuckles' theme song , "Unknown From ME", contains the line "Wild and hungry ain't a damn thing funny".
In the first Sonic Riders, tricks you do are named and S rank and higher trick combos unlock character specific moves. A lot of these are VERY suggestive, such as Rouge's aforementioned Sexy Shot move and, in what HAD to be the result of assassinating the censors, Wave's easy-to-perform signature move: Double Swallow
Inverted. in Sonic the Comic, at first the writers almost got into a lawsuit once due to the fact they weren't listening to their guidelines, but later Sega stopped paying attention. Thus the writers were given a major amount of freedom that other adaptations weren't. Sonic and friends could be in the presence of alcohol (not a G-Rated Drug, and they refused to drink it though), one arc was name "Village of the Damned", and violence was abound (though oddly bloodless).
In one of the old Sonic Grams online for the comics, Fiona and Scourge have this exchange.
Fiona: Time for bed, babe.
Fiona: You wanted the letter, remember?
Thinking about his character, what else might he have wanted?