Should you tag him? No. I would report a couple of those posts to the moderators with a note telling them what he's doing, which is spamming. Let them take care of the problem, which will likely result in the account being banned. I seriously doubt that member created an account here to do anything other than promote whatever it is he's promoting. Giving him a tag is just a useless gesture that won't solve the problem.
A warning on his profile could be Ok, a neutral for now as reference perhaps.
Nah, it might not be against the rules to do that but it would be far better to report this crap to the mods.