Yes, it is allowed.
Like vague rule number 1, "1. No zero or low value, pointless or uninteresting posts or threads."
That's the thing. People with multiple account or even just one account in a sig campaign creates a lot of these posts.
You see it almost every time there's a new topic: entire pages filled with one-/two-liners, all adorned with a lovely little signature advertising some gambling/trading/ponzi site. And all of hem are usually iterations of the one guy that actually posts an answer to the OP's question.