hi, it help.. if signature are from good pr posts like 1 2 3 4 or even index by search engine posts then its help you a lot but don't rush ... keep it slowly ..otherwise its come in sense of link farming ..and even some forum get you banned ...
Signature is one of methods to increase PR, not to mention there's a big chance being removed by the mods if found out you're just spamming
No, because the pages on which you will post have no PR or PR0. PR from the main domain will not count. Forum signatures are only good for faster indexing.
I would say 100. That was when I started to see the DP forum postings show up in my link counts at GWT or YSE.