This is a Sonic Mania poster from the online Sega Shop.
The Sega Shop is probably the only place this is released in 2018. It's standard poster sized (so, big) & fairly simple, with the Mania logo large at the top and the neoclassic 'box art' for Sonic with geometric shapes as the main design on a yellow background. This is probably what they were thinking the 'box art' would have looked like, had the game ever been a physical item.
It's been seen before, but it makes for a stylish game room poster with plenty of bright color & a good action pose for Sonic. It should be 15.95 at the Sega Shop website.