My votes go to:
Kudaranai: Interesting concept, the signature gives a sense of realism while still maintaining the appearance of being... what's the word I'm looking for... cartooned? I dunno. I like it.
Pshfrk: While the color choices need some work, it comes together very well as a signature. Excellent depth, and the relation to the theme is interesting.
Glarbage: One of these looks like a signature, one of these looks like a page from a photo album. Just saying.
Noperative: I like the concept, even if the depth is a bit confusing. :x