I've read in a few places that having a bunch of one way inbound links from places un-related to your website makes it harder for the search engines and spiders to determine your website's theme. What I did in the past was put a link to my website in my signature that I used on a few un-related message boards. I cannot get any of the search engines to register my key words, so I just deleted these unrelated links. Did I do the right thing by deleting these links? These links did have my keywords in the anchor text however.
If the links have your keyword in the anchor text, they wouldn't have harmed you. Note, they wouldn't have helped you either if they were just junk links from totally unrelated sites. Forum signatures do get a discounted link value so they aren't worth as much as context links. Focus more on quality inbound links. Forum signatures do help sometimes if they are from forums like this one google finds you more sooner than putting a link to your new site somewhere and waiting for google to find you. Nothing i'd worry about..just build more content related one way links