Ah, from there? I see... but you know, you can use practically every single avatar from there, even if it exceeds your current avatar size limit! Just pick any one that you like and resize it with Photoshop (or even Paint) to 100x100. XD
As for signature, I think I'm good with my current one. It's all text, and small text at that... but I like to keep it simple, hehe.