Bee Playing Cards with Tax Stamp

Hi! I found these cards in a box of things my mother gave me. I was going to let the kids have them but noticed that they were still sealed with a funny stamp and thought I should ask first. The stamp says U.S. Int. Rev. so I am assuming it is a tax stamp. I tried to look them up but haven't had much luck. Just wanted to figure out if I can throw them in the kids game closet or should i put them up for safe keeping.