Communications are vital in any tactical operation. Sometimes, due to the necessity for stealth or simply the need for quick signaling, operators need to use hand signals.
There are many signals and many different signals for the same message depending on where you look. What ultimately matters is that everybody agrees on a set of signals and sticks to them. There has been a recent trend towards standardizing tactical hand signals for SWAT teams. This makes operations with other agencies in large operations easier and in the event of a mutual aid call out can help minimize miss-communications.
Below are a few examples of hand signals that are fairly common and pretty consistent regardless of which system you use.
Get Down/Find Cover
Cover (my move..area with fire)
Do not understand