There's a link to Steam's forum rules on the right hand side of just about every page called "Discussions Rules and Guidelines", and there's an expanded version at the link below.
https://steamcommunity.com/sharedfiles/filedetails/?id=143962136
They're quite simple, common-sense rules, but please check the list below for some forum-specific clarifications of those rules.

1. Do not flame or insult other members - Don't mock or put down others, treat everyone, including individuals who post on these forums as well as those who do not, with respect at all times.
   
2. Do not bypass any filters, or post any content on containing abusive language, including swearing - If you're using bad language in any way, don't. The censors are NOT a security blanket that allow you to swear/curse without reprimand. Posts breaking this rule will be removed, but re-posting without the bad language is allowed.
   
3. Do not bump threads
   
4. Do not post spam (i.e. +1, 10char, rickrolls) or Re-post Closed, Modified, Deleted Content - So if a moderator removes your post/thread, don't post it again. It was done for a reason.
   
5. Do not openly argue with a moderator - If you want to discuss something, ask in the thread for a PM so it can be discussed in private. If you've been given a warning/suspension/ban, you have that PM channel already.
   
6. Do not post any content containing cheating, hacking (including modding), game exploits - This includes "callouts" against those using them under the flaming rule above.

Also, from Steam's guide to the rules:

Originally posted by Steam:

Naming and Shaming

Why is naming and shaming not allowed?
The Steam Community is not a place to do this. One reason is that claims can be falsified. Anyone could potentially create false information about another user and encourage report abuse based on that information.

Instead of creating naming and shaming topics, use the provided “Report Violation” functionality located on a users profile to report suspected scamming or other abuse.

For further insight into 2K's interpretation of Steam's rules, please see the official 2K forum's rules[forums.2k.com].

The moderators of this forum are not employees of 2K. We're simply volunteer members from the official forums tasked with keeping the forums clean and tidy. As such, we can only know as much as you or anyone else posting on the forum.