Up for Grabs. I'm not sure if there is a trope at all. A Gavel is a little mallet that probably many people associate with a judge and an auctioneer. But on several occasions I have seen that they are used by the chairman of a meeting e.g. Mayor Quimby from The Simpsons uses one on Town meetings. Since I'm not familiar with gavel use in general I wonder if this is a trope at all.
Hello, Unknown Troper. You'll need to get known to lend a hand here.