The forums are simply for exchanging information giving and recieving help. Simply follow the content guidelines in the descriptions and be friendly you can't go wrong.
Signature files and urls are allowed - spamming by abusing the sig files, putting affiliate codes in links, not disclosing personal information about relationships to products or website services when relevant (eg you make the product, run the service or have shares or a friend or relative does). And any other form spam i have yet thought about - its a sort of know it when you see it thing.
Flaming, trolling, the usual annoying crap which turns people off forums won't be tolerated. Useful critical comment about things, images etc are welcome please try and do it in the right spirit though.