Ups, sorry for few mistakes and thank you for info on signature campaign. At some point I will stop advertising for free :-)))
I actually did a bit more reading about the rules of different signature campaigns since I wrote that and each one is slightly different but I'd say most allow for rolling over of posts. The old PrimeDice campaign definitely did if you didn't reach the minimum limit of 50 posts per month and once Stunna reopens his campaign, it should do so as well. ActionCrypto (currently closed) also rolled over previous weeks' posts if it was under the minimum limit of 20 posts but in order to receive any payment, you had to make 20 posts in that week. So if you made 10 posts in week 1, 15 posts in week 2, and 20 posts in week 3, you would get paid for 10 + 15 + 20 = 45 posts in week 3. 777coin and Bitin.io don't allow for any rolling over of posts except for posts that were made in the first week. Bitmixer.io (closed for new participants) doesn't need to roll over posts since they don't have a minimum limit.
I also remember there was another campaign that had a special program for those who posted very infrequently. I'll see if I can find it...
EDIT: OK, I can't seem to be able to find it but BIT-X seems to have no minimum posting limits. But you will need to wait until you are full member to join.