Specifically, you are not allowed to give people any incentive to post insubstantial posts in your threads. You can't offer to pay people who post their addresses, usernames, etc. You can do giveaways off-site and link to the giveaway page in a thread, but you can't give people any bonus for replying to your thread.
And the following is taken from mprep's
thread:
Anyone posting info from their bounty application (usernames, addresses, etc.) or anything alongside the lines of "joined X", "looking forward to getting X", "thanks for the opportunity", "filled out form", "signed up for X", "applied", "following / liked / retweeted X" when such data is not required or the requirement is against the forum's rules risk having their account banned. These are extremely low quality posts generate massive amounts of spam, drowning out any legitimate discussion these threads may posses.
I have already been sent a number of PM's regarding users who post 'reports' for Twitter/Facebook bounties. Example is below:
This should be disallowed, right? If the bounty threads are requiring this kind of reporting then it's simply another form of incentivizing posts on the thread. Another way of just 'bumping'.