I like the simple forum as well but I don't think a small space for a couple of rows - maybe a bit smaller font size and lighter color even - would distract anyone from the discussion.
Signatures have been a part of the biggest forums since many years, for example vBulletin, phpBB, etc.
It would be nice to have a small space to share some info or thought..
Example
I'm working on project X, would love some beta testers. Signup
Signatures are just an opportunity for spamming in my opinion. Add nothing to a conversation other than a space for the post author to advertise themselves or something they’ve involved in.
Spamming alert !!! There is no good reason for this except for self-publicity. This leads to poor "me-too" answers to questions just so that links can be pushed out.
Has nothing do do with spamming, that is done anyway. If not abused, it's not a bad idea. But two sides of every coin, a call for beta testers could always be put right into the post as well.
A wise word: There are the overly serious people, and the Saturday Night Live sense of humor type. The latter is usually happier. Also 500 years from now there will be no difference in the two. Spoken by a truly wise man.
Hmm, I'm not sure I see much value in adding signatures. I think most forums are so ugly and bloated. For now, I'd prefer to keep things as simple as I can.
I do not think it is necessary, that is so old school and a spammer delight. I would vote to not change the present clean design...if I had a vote. In short, I personally do not want to view your advertisements whether they be for business or personal...your username will suffice. It would be like reading every Twitter retweet that spam my timeline.
We all come here for answers or to help others. Signatures are just a distraction. I've always like how Stack Exchange does it. If you just HAVE to do something like that, you can put it on your SE profile.