I agree. Sometimes I feel their signature is part of their post (like a pictorial guide on how to hack runescape) but then I realize its just the poster's sig. There is no need to have huge sigs that are 100x larger than your posts.
Examples:
http://ezud.com/forum/showpost.php?p=22859&postcount=20
http://ezud.com/forum/showpost.php?p=22435&postcount=5