A mint in the package post card!
This could be in a clear wrapper because it's actually a set of multiple post cards...or...someone could have just shrink-wrapped a single card. It's a Sonic Adventure 1 promoting item, with the logo 'watermarked' really big on the back along with the Dreamcast logo. The front has that 'circular walking' sort of odd Sonic popularized via SA1 promoting, the Life of Power quote (small) above his name. It's otherwise pretty plain.