There's footage of a proto-type build of Sonic in the background of the Noah's Arcade ad in Wayne's World. The footage shows UFOs in Marble Zone. These UFOs were removed from the final build of the game.

In issue 260 of Nintendo Power, Yuji Naka revealed that the initial concept for Sonic the Hedgehog's gameplay came from playing level 1-1 of Super Mario Bros. over and over again as fast as he could, since you always had to play the level first regardless of whether you used warp zones or not.
"I always tried to get through the level as fast as I could. And that inspired the initial concept for Sonic the Hedgehog."

The title screens of Sonic the Hedgehog and Sonic the Hedgehog 2, with Sonic (a character known for his super speed) posing and waving his gloved hand inside of a ring lined with stars and a ribbon banner at the bottom, could possibly be taken from the logo of the 1981 anime adaptation of the Akira Toriyama manga "Dr. Slump" and its speedy protagonist Arale. It should also be noted that the ring surrounding Sonic has giant wings protruding from its sides, which appear to reference the angel wings on Arale's cap that also feature in the intros to the anime and some of the Dr. Slump films.

While it's not known if any Sega employees have commented on this connection, it was acknowledged in the form of a small cameo appearance where Sonic gets outrun by Arale in the 1993 sequel manga "The Brief Return of Dr. Slump".

It's possible to play the game using an Atari 2600 controller, as every button besides start works as a jump button, and thus the game is fully playable despite the controller only having a single button.

The appearance of Longclaw in Paramount’s Sonic the Hedgehog films is reminiscent of the tiles that resemble an owl's head in the Labyrinth Zone from the original Sonic the Hedgehog. In fact, the first film's opening scene features the tile design engraved on a rock as an Easter egg, further hinting at the connection.