Here are 6 more Sweat Shirts from the Sega Shop in the fall of 2018. Each one is a hoodie, and is adult sizes only.
The first one is all black with a red "Eggman Empire Mark" graphic (seen elsewhere in more detail) The next 2 are just variants of eachother with opposite color red/black graphic and black/red graphic. These have the Eggman Empire logo from Sonic Forces.

The fourth is the "Gold Crest", which is the detailed yellow line art of modern Sonic in a 'radiating lines' ring shape with curved Japanese text down one edge. The last two are variants again, either blue or white. They have the same design in the same colors. It's the classic logo with Sonic portrait & the numbers "9 1" there are two 'midway goal post' things in their 'mid hit' position sort of criss-crossed to represent/break up the "1991" although that's slightly confusing. As usual, they're 35 to 40 dollars each.