Let me tell you why accounts gets banned, Basically there are some Rules in the forum if you Break any following rules you will be banned.
Breaking all of these forum rules does not lead to a ban. AFAIK sharing malware and plagiarism are the main reasons that could get an account banned.
Breaking some of the other rules could mean your post/thread will be deleted/trashed.
Signature spam is a bannable(temporary for first offenses and then increase in duration till a permanent an is issued) offense, but the rule is barely enforced.
You should note also that newbie accounts (below 30 activity) can be nuked for a variety of reasons.