Where is the serial number on a sears model 101.25 .410 3 inch bolt action shotgun that's the same as a Stevens model 39 or 59?

It was made before 1968, and wasn't required to have a s.n. Most inexpensive guns didn't, as it only added to the manufacturing cost.

THANK YOU WHOEVER YOU ARE, AND YES THEY WERE INEXPENSIVE, SO MUCH SO A DIVORCE' GAVE IT TO ME JUST TO GET IT OUT OF HER HOUSE. CAN'T BELIEVE THE CRAZY ESTIMATES I SEE ON HERE FOR THAT GUN. THANKS AGAIN.