The Sega Shop's theme for fall 2020 is "Sonic Graffiti".
This sweat shirt is part of that line, and called "Emerald Club Graffiti Crew Sweat Shirt". It's about 40 dollars in the Sega Shop (online only) and also only in adult sizes. 40 seems pretty typical for an adult sweatshirt at this point so...normal. The shirt is a plain mottled gray, except for this design in the middle of the front all in white...except...for that one "Emerald Club" diamond shape there at the bottom which is done in black. It is a curious detail.
The design is a montage of Sonic faces, phrases, logos and shapes done in various fonts, stencils and shapes. You can spot "Ring Collection Association", Let's roll, Too Easy, Gotta Go Fast, Tails, Zone, Step it Up, Sonic Speed and How I roll. There's also a drippy eggman face & some lightening bolt shaped arrows.

Even though it's clear the design is just a single front-stamp on a sweat shirt, the chaotic and collage-like nature of the design keeps it looking fresh and different. There isn't another product out here (from the past) that looks like this.