I actually think both blog comments (especially if moderated) as well as forum signatures are good ways to build your first 1,000 links to your site so that others do not copy them. I think most people when they are looking to copy backlinks are looking for the easiest and highest quality links. Neither technique you're talking about it adding an incredible amount of value (I don't believe they are worthless though) so another webmaster is not likely to attempt to copy them.