They actually help for spammers sometimes by keywords taking google hits AWAY from actual content. An example. Type this into google. I did...
"Just a lone patriot acting alone at a fulcrum point" site:socnet.com
It's a forum that I read. The above quote was from a thread on I forget what, but I wanted to find it again because it was an interesting thread. I can't find the damn thread because it's hidden among thousands of hits because someone besides me liked that quote and stuck it in his signature line. Now the guy who did that isn't a spammer, but it's a long-used spamming technique, to the detriment of the forum itself.
and may be annoying to some folk.
See above. I can't find the actual content due to this and I would like to. Again, the guy didn't intend to be a spammer, but the effect is the same.
My view of a positive use of signatures would be to start "AssertNull's Computer Consulting" and stick a link in my signature. Or a link to my programming blog. Those who find my programming help useful could click on it. Those who don't wouldn't. That's win-win-win I believe (win for me, win for the link clicker, win for the forum). The link would be relevant to the forum and non-invasive. If I add a symbiotic backlink baack to Daniweb, then you have related content endorsing each other, which is the spirit of backlinking rather than quid pro quo. Folks who find my posts useful click my sig because I've earned it. Daniweb appreciates quality posters and rewards them by offering that signature to get traffic to their site. And I would link to Daniweb. Again, symbiotic and a tip of the hat to quality. Google sees this and ranks accordingly. Someone googles "C++ pass by value" and both sites benefit.
That's how it's SUPPOSED to work, I feel. There are no "tricks" involved. If I start posting garbage just to increase post count in order to get more search engine hits, that's spamming, and hopefully that would drive people AWAY from my site. They certainly won't be clicking on my sig.
The thread RProffitt shows IMNSHO the way it SHOULDN'T work. One poster commenting has a signature that is for Chinese food. This is a technical thread on a technical forum. Even if I thought the poster gave good technical advice in that thread, which I do not and apparently no one else did, I'm not going to click on a "Chinese Food" link. I see no reason to have that kind of sig on Daniweb except as a spammer, and checking out that person's posts seems to bear that out.
I'm no expert at all in search algorithms, but I've talked to some folks who are and they told me that Google has tests to ferret that out and flag it as spam and when that happens, the signature site is flagged AND the forum is flagged.
What Assert said. I put a link to my website in my sig, I don't force anyone to click on it and I don't post just to try and get those clicks. Would I care if the sig facility was declared illegal by that <irony>very sensible</irony> Trump chap? Nope, not at all. Would make forum moderating a whole heck easier and wouldn't hurt genuine sites with good content either.