Currently, there’s no way for me to show that I like using Haskell. Could there be a functional programming or Haskell tag?
There is already such a thing through the achievements: there are Haskell related achievements and there are also achievements for finishing in top 1,3,5,10 in your language in a contest. Might not be what you’re looking for though (registration for contests/profile page) but it gets pretty close.
Also, FP is not only Haskell. And this is a Haskell guy writing these lines.