Keep this Coupon

It's not any type of coupon as I understand the word.

It has no discount listed, no manufacturer or product code

no restrictions written on the back

nothing written on the back

white

one fat thumb tall

two wide

KEEP THIS COUPON 627545

the 627545 part is black font printed vertical

while the KEEP THIS COUPON and the surrounding rounded rectangle is a royal blue

I found it on the ground

Someone failed to follow the instructions

now I have to 

what would happen if I didn't?

I wish I knew for how long, or for what purpose - but that's my lotto in life