We always leave a cash tip and I am always a little worried that someone will take it. I usually will put it in the sleeve with the bill. And sometimes call the waiter/waitress attention to it, if it is on the table.
Well, I always leave a cash tip and do the same: call or nod to the waiter that I/we are leaving and there is money on the table.
AND THE MOST IMPORTANT PART (after being a waiter and bartender in college): NEVER LEAVE MONEY WHEN THERE ARE obama kids AROUND. Yes, I said it and seen it multiple times. They STEAL money.