Look closely and you’ll see the big goofy grin of a comic strip that very closely resembles Charlie Brown.  This misprint can be found on some Sapphire, Emerald, and Ruby Medallions.  It’s also worth noting that these are known to exist in English, German and Portuguese and have yet to be found in French, Italian, Japanese, Korean, Spanish, or T-Chinese.

These are the Charlie Brown Medallions.  It's worth noting that it's possible that the comics on the emerald and ruby are not from Peanuts, but the clarity makes it too difficult to identify them.  I've compared actual Peanuts strips to the markings on these cards to try and find the exact comic, and have been unable to find it.  Its very likely that if it is Charlie B on the cards, that it's not a printed version from a comic strip.

I've done a quick and dirty trace over the misprint if you've had trouble seeing it.  It's not exact, but it'll show you the general spots and shapes to look for when identifying Charlie Brown medallions.

Why not animate it too?  The compression kinda kills it, but you can click on the gif to make it larger.