Apparently, you can trademark SMELLS. Even ones that aren't particularly good, I guess.
Hasbro just announced that it has successfully trademarked the smell of PLAY-DOH.
They described the smell as a, quote, "sweet, slightly musky, vanilla-like fragrance, with slight overtones of cherry and the natural smell of a salted, wheat-based dough."
We might've gone with "yeasty, sweaty feet," but hey, whatever you say, Hasbro.