MLB Gold Card Question

RighteousRyezelle

Hello Friends,
I've come across some MLB gold cards that have serial numbers on the back. I can't find any others that have been serial number stamped like these. Any thoughts if these are extremely rare or if someone did these themselves after receiving them or something else?

Thanks,

Zach

Not Serial #'d look like this:

Cards I found with serial numbers:

Ridethelightning

Lick the back of those. Dude. Serious. You will become 'aware'. You can then sell to others to lick the back of. 50 quid'a'lick'.