tcpdump command line switch to show packet counts?

This is my first question here so bear with me. It's a simple question:

In tcpdump there is a command line switch that causes the system to show an ongoing packet count as packets are captured. I've seen it in use but cannot remember and the docs don't say. Without it you're left to stare at nothing and don't really know if packets are being collected.

What is that switch on an F5?

Thanks