Here is a deck of ordinary playing cards.
It's not surprising to find Sonic on something as normal as a deck of cards, in this era. Notice the Segasonic branding there at the bottom, placing these in the 1990s. The card backs are all green, and all the same. They have the nice, fully shaded finger-waving Sonic art. He is standing in front of a darker green circle, with black/white lines/textured 'ring' shape around it. The borders are white, and the card faces are all completely normal. There's nothing else 'Sonic' about the deck, other than the card backs.
They're shown here in the original bag packaging. These are likely to be a Segaworld item in Japan, but it's not 100% known.