Marvel Studios has escalated a Thunderbolts* plot point into the real world by adding a copyright symbol to several official Avengers social media pages. To explain the reason why and what it means, we'll have to get into some spoilers for Thunderbolts* (but nothing Marvel Studios hasn't spoiled itself).
Thunderbolts* ends with the asterisk turning the title into New Avengers, as Marvel has now spoiled by releasing a poster with the updated title revealed in place of the original logo.
