Many of the sports books are doing this and like I said rollbit is a casino with a multitude of games on it, not just sports betting. In other words sports betting is not the only thing in the focus but many other casino games too. Recently they started the PvP duel arena section and that too need promotion which they are currently focusing on. They started a new signature campaign for that with same payouts as the original.
Rollbit did not have sportsbook when they created their announcement thread in bitcointalk and they only launched it recent months maybe not longer than 2 years after taking community request seriously. After they agreed to have a sportbook on their platform, they started to build it up and I recalled this took a few months for them before launching.
Maybe in near future they will campaign for sports but not at this point.
It is interesting campaign from Rollbit team if they do it but I think they can promote their sportbook by creating some different signature sets and allow their signature campaign participants to pick what signature design to use. Who like sports will choose sportbook signature to wear for their account.