After sleeping on it a little, two examples of things that are typically used on the field(s) I'm on.
A pretty common one used on a LOT of fields and between a lot of different crews is the arm extended overhead, index finger pointing up, rotating at either the wrist or shoulder in small circles.
The purpose of this is typically indicating that "what I can see of your players is clean."
A similar gesture is rotating your finger pointing towards the ground, signaling "I heard your all clean." though this is accomplished slightly more efficiently with a simple nod of the head.
Pertaining to the new PSP rulebook for 2013, "If the last player on a team is eliminated by a major penalty, the game is stopped and the opposing team receives a point."
Keeping the body count straight across the field, or more importantly, are there any bodies left after a penalty is assessed. This becomes exceptionally difficult when the penalty happens on the Dorito side and both bodies are assessed on that side of the field. Without the referee on that side of the field running to the snake side of the field and seeing there are no players laying belly down and out-of-sight in the snake beams, a quick signal across field can save time on the clock for the players as well as spare referee extra running across the field.
An example of this that has been used on fields I worked on in the past is raising both arms in front of your body, elbows bent slightly and hands open, rotating both hands at the wrist. Typically, this is performed first by the referee assessing the penalty and checking to see if the clock needs to be stopped. If there are no bodies left and you are CERTAIN, the responding signal is to call for the clock to stop, or arms over head clasped at the wrist.
Just a few examples of what I have seen and what we have found useful in the past.
CFOA/PSP Certified Referee