These are called "Mania Plus Character Head", and, interestingly enough, the sweat shirt's variant is a tee shirt. They're both black & have the exact same design of Sonic Mania Plus character heads all set in profile. There's Sonic, Tails, Knuckles, Mighty & Ray all in a little row. They look like colorful icons across the front/chest of the clothes.
It's a tad plain/simple, but the characters are fun and colorful & the style is nicely in keeping with the classic look. The tee is 25 dollars, the sweat shirt is 40, and both are in the Sega Shop online in 2018.