Were you born on the 31st, do you live on #31, or have another special connection with 31?
 
Then these small badges are great for you!
 
These chrome badges are about 30 mm in section, have a  thread with nut and washer on the rear and come in a cute box with instructions.
 
Made in England, presumably in the 1980s, these are still unused and thus excellent!
 
One set only, so first come, first served!