It probably means that the pin is made of 10 karat gold, and that KB is the trademark of the manufacturer. However, before listing it, to be absolutely sure, you should have it tested for 10 karat gold.
I stand corrected! Owl is correct, as usual.. The letter B is probably the trademark, not KB. The letter K is part of the fineness mark (10K) which of course stands for Ten Karat gold, or 41.7% pure gold.