I looked it up. Google says you shouldn't have optimized links in the post or the signature.
For example, a signature that looks like this, with links to your website, is probably a no-no:
Sponge Bob Pillow Cases | Sponge Bob Toys | Sponge Bob Books
I guess it might look even more spammy to Google if such a signature were on a sporting goods forum because the content doesn't match the signature.
But, if I were on a parenting forum, I would definitely use a signature like this:
Sponge Bob books, toys and other goodies for kids of all ages!
In any case, I've run a bunch of websites in my day. Never really cared about PR, because I focus on making money. I don't make Google my #1 priority because I don't want to be a slave to their rhythm. Oddly enough this "I don't care attitude" has paid off. My sites do well in Google - and even more importantly, they do well without Google. That's how you build longevity.