Took me about a minute to identify it is a yo-yo (without reading any of the discussions), and they point out there that the official ball has a yo-yo for Y, so

Took me about a minute to identify it is a yo-yo (without reading any of the discussions), and they point out there that the official ball has a yo-yo for Y, so I am quite convinced that it is supposed to be a yo-yo as well. Just not drawn particularly nicely: the yellow bit is a cartoon string, the blue-and-white bit is the yo-yo's "body". Edit: although now that I finished reading the rest of the investigation, there are quite a few arguments for "yxa" as well. Still seems like an odd coincidence to see a yo-yo there myself, and then to read that it is supposed to be a yo-yo on the official ball.