I know that extra signals are something that is frowned upon by the games under the aegis of the USSF. However, would it be appropriate in the pregame discussion as a assistant to let a center know that you are going to put your flag halfway up; that is running with it slightly raised as opposed to down at your side? The biggest trouble I am having with players or fans is when I am waiting to determine if the player in an offside position or the player who was not in an offside postion(at the time the ball was played to them by a teammate) will make the next play on the ball.
USSF answer (June 24, 2008):
We are not certain that this unofficial signal would do much to help you. Our fear is that it might confuse everyone, the busy referee, the players, and those wonderful spectators, by suggesting that the flag was about to be raised the entire way in the next instant. We recommend a wait-and-see posture instead.
The Federation does not necessarily frown on unofficial signals, but the USSF Guide to Procedures for Referees, Assistant Referees provides a set of standard signals that should not be changed lightly — other signals may be used provided they meet certain criteria (spelled out in the Guide itself).