In which arcade racing game did Sonic first appear as a mirror ornament?

Sonic first appeared as a mirror ornament in the arcade racing game Rad Mobile.

Rad Mobile was developed by Sega AM3 and released in arcades in 1991. It is a 3D racing game in which players drive across a long route while dealing with traffic, weather, time limits, and changing road conditions. Its use of a rearview mirror helped make Sonic’s cameo especially distinctive: he hangs from the mirror as a small ornament inside the car.

This appearance occurred before the release of Sonic the Hedgehog, making Rad Mobile Sonic’s first video-game appearance. Sega allowed the racing team to use the character partly to increase public exposure for the new mascot while Sonic’s own game was still being prepared.

A frequent mistake is naming Out Run or Daytona USA, both famous Sega racing games. Neither is the answer here. Rad Mobile is the important title because it introduced Sonic in cameo form several months before his platform-game debut.