Ever since Twitter made Likes privates, many users on the gaming side have been replying to posts with, "Yeah!" to express their support on specific posts. The origin of this trend stems from Miiverse, a social network created by Nintendo for the 3DS and Wii U. "Yeah!" was the Like equivalent for that platform.
However, the trend seems to be gaining much more traction than expected, and it's even reaching non-gaming Twitter:
However, the trend seems to be gaining much more traction than expected, and it's even reaching non-gaming Twitter: