Some dev not allowed newbie join their bounty because they scared if too much spammer , and make their project bad quality.
But newbie can join a twitter or fb bounty , a lot bounty rules for social media is allowed for newbie.
But if signature campaign bounty is not much , but their dont want newbie join because their dont want newbie spam on this forum for raise post count or activity.
I recommend u join a airdrop or social media bounty the distribution/allocation for twitter and fb average with Jr.Member signature campaign.