Generally speaking they are, though it's not a definitive rule and Global moderators can give any duration they feel appropriate for the deed. Permabans are sometimes given out without any other warnings for copy and pasting and sometimes users who's accounts have posted nothing but low quality spam. I rarely give bans out for signature spam these days though as it's the people who are running the campaigns that should be getting them. Can't win a war against a hydra that is spawning thousands of hydra parasites everywhere.