1script - 4:46 pm on May 13, 2013 (gmt 0)
THAT would make you look even more like a spammer. Most spammers are not interested in building local following at the forum site and only register to have that one profile link. If you were a member for years but all you have is also that one profile link, you will look nothing different to Google than a spammer that just registered a second before Googlebot hit.
Re-tool the signature code so that the link on the member's profile page is the only external link and their massive internal forum contributions that built value for you over time (compelling content) is rewarded by providing their profile solid link juice.
Many profile page URLs are robot disallowed or noindexed just for the very purpose of discouraging drive-by registrations for link dropping only. I do it on all forums I support. I don't know exactly how Google treats signature ULRs on forums but it's pretty clear to me that if you are consolidating all of your forums links from that site into one profile URL, you might as well just simply delete all the links.