I'm really sorry, but sig links are definitely NOT spam.
You'll be surprised to see how many people will check the sig URL of a person that gave them a profound answer. If they check the link, and see something they like in my shop - that is something called great marketing.
There is absolutely nothing wrong with that. And if there was, FTR would have canceled sig links a long time ago.

Note that I own the site, and I contacted this person myself (picked him from many other forum members). Unfortunately I bumped into the wrong guy, but it doesn't change the fact that it's still a win-win situation.

And yes, maybe sending private messages isn't the best way to reach forum members, but I don't know of any other tactics.

+

You usually don't reply to SPAM messages, right?