I am sorry but you really got to work on your profile first before enrolling in signature bounties.
Consider the example of a new person who has recently joined bitcointalk and is asking for advice. Would he ever trust advice of a newbie user over advice of a Senior or Hero member? Hence, 99% of the campaigns wouldn't let newbies participate in them.
You have to be at least Jr Member in order to be eligible for most of the campaigns and at least a Full member to be eligible for all the campaigns.
With time and effort, you would be able to reach that rank.