I think some new "airdrop" gifts are very close and I'm a little confused as to how the recent Sig / Bounty campaign has been discontinued while some very sketchy airdrop threads have been able to uncheck.
You can give off-site and link to a page in a thread, but you can't give people a bonus for responding to your thread.
If people want to give away, at least give it away on their own site or in a place where it can be done. Create a section to give coins maybe to keep the content in one section and not everywhere.