Is it beneficial to your site to have your link placed in several forum sigs? Would it boost up your PR is anyway?
The links do get indexed by Yahoo, I know that much....they're probably worthless unless it's on a forum related to yours, and even then I doubt they have much merit.
Ya, it will probably boost it up quite a bit. I've done a few sites where I got site-wide incoming links and I got a PR6 from a PR0. I don't really care what the PR was, because it's all about traffic, and not PR, but that's one thing Google seemed to like, was site-wide's to get high PR.
It is beneficial to have your sites in your signature, because it will give some traffic. Won't help much in link popularity, but the more links the more exposure to your site. If site topic is same as forum, you will see beter results.
I dont think forum sigs would count towards PR, but they can help search engine spiders find your site better and thereby more likely to fully index the site. Signatures should not harm your site, but will not generate a lot of traffic either... you may get the odd interested person visiting a site in your signature out of curiosity. Overall, it is normally untargeted, low quantity and therefore almost unecessary - apart from possibly helping to get indexed deeper.