As antoine and ioc said, Google won’t reveal all backlinks with the link:example.com. Use Yahoo for this (with the same command).
Google knows about your backlinks, in order to check them, sign up with Google Webmaster Tools, go to Links section and “Pages with external links” and there you can see the incoming links to your pages. (Click on the underlined numbers to see the exact websites that link to that given page).
Oh, and forum signature links have very small impact when Google counts your backlinks’ weight.
Hope this helps. 