Basically each guest at the shower is greeted at the door and is handed a safety pin (can put cute baby related items on the pin like mini pacifiers, etc.) I've also seen a clothespin variation, hot glued plastic babies on pins, etc. The guests place pin where it is visible and then are instructed that certain words at the party are taboo (common words you are going to hear regularly at a shower like baby, pregnant, the baby's name if it is known etc.) As guests wander around the party (this encourages them to mingle) they listen for others to use the taboo words while they try themselves not to use the words in conversations, if anyone says a taboo word they give up their pin to whomever caught them. Whoever has the most pins at the end of the allotted time or the end of the shower is the winner.