dropped 3rd strike mechanics

[YoungRighty]

Let me restate my question using an example:

R3, no outs, two strikes on the batter. Pitch is a low curve ball, batter swings and misses, catcher raises his mitt with the ball and lots of dust. In other words, it's not obvious if the pitch was caught or if it bounced. The batter takes off for first. Now the catcher has to decide whether to throw to first or not. Shouldn't my call be clear enough to let him know immediately whether he must throw to first or not? He shouldn't have to risk a bad throw (and a run scoring) because he couldn't clearly and immediately recognize my call. It would be analogous to a base runner trying to figure out if a sinking liner was caught or trapped - he's taught to look immediately at the umpire to get the call.

What should the catcher be looking for in my example? If I judge that the pitch has bounced before he caught it, how do I indicate that fact? If I judge that the pitch was caught, how do I let him know that?