Well guidelines are rules per se, although often used in a less stringent context.

Campaign managers are advised to ensure to quality of posts made on their project, and we can go back and forth about whether BTC paying signatures gets more attention, but as long as it's an attempt to curb spam, then it can't really be a problem.
BTC signature campaigns usually have fewer members than regular ICOs and hence it's more possible to manage and regulates the quality of posts made.