Hasbro has trademarked the smell of Play-Doh.
It may sound weird, but, as we all know from our study of intellectual property in the legal area, you can trademark any distinctive name, shape, colour, or other factor that uniquely identifies your product.
Not surprising. Lots of features can be considered a key part of a brand in people's minds. Harley-Davidson trademarked their unique exhaust sound in 1994.
I think the first smell trademark was filed before that in the late 80s or early 90s.