Signatures are an awesome feature on forums, and I would love to see this implemented on MPSocial. Its a great way for me to add some useful snippets of information, and who knows what else.
the only problem I have along with many others is that Signatures can get pretty messy, and make the forum look tacky. So if you proceed with this, maybe something simple with some restrictions as to what can be added. Maybe just plain text without the ability to add gifs, and other pictures would keep things clean looking.
Just my 2 cents