[Adam]

Just raise your fist for a foul; don’t do a prelim (if you're calling a flagrant, everyone knows what just happened). Once you have the players under control and your partner is able to keep them under control, walk all the way to the table to tell them what you have. Then tell the coach you've just called the flagrant, and "why" if you feel it's appropriate and necessary. There's no need for signals on the court.

Now, every flagrant I've called was for an actual fight, so a signal wasn't necessary. We just got the players separated, sent them to the bench, got together to collect our thoughts and make a ruling, and walked to the table to report it and called the coaches together to let them know.