If you are newbie then you need to keep posting, and then one day you will reach a higher rank. When you have a higher rank you can join signature bounty.
But there are lots of different bounties, you can do twitter, blog, translation or video.
I agree, eventhough you are a newbie it doesn't mean you can't join in bounties. There's a lot of bounties that you can join in your rank. Like twitter and Facebook campaign. You can join also in telegram. You just choice a bounty that accept a newbie.
I think a lot of bounty that accepts newbie rank with the requirement to follow social media or blog and media content.
but remember if the rules should still be followed to qualify for a weekly reward.