I think it’s more common to check if their hair looks suspiciously like yarn.
This is still the rule, AFAIK. They don’t mind explaining to you in a PM, they just don’t usually do it publicly.
I don’t think this is usually true. There are any number of banned socks or trolls that you can still see all their posts and read their profiles.
If the thread was corn-fielded, it’s probably something like a returning banned poster who has socked up multiple times. Yes, this is apparently a common thing, one that I don’t understand at all.
At any rate, just PM a mod from that forum, they’ll tell you what it was about.