I dont think there is anything wrong in joining a Signature campaign even as a newbie as I am even wearing one although the amount earned will be small but its something which can be used to build up the rank and at same time learn one or two things before ranking up to make higher coins. Also dont forget when one ranks up and then apply there is a kind of background check to about the quality of your post even before accepting into the campaign even me as a newbie I have been rejected several times.