"No Shot "Mechanic

[Troward]

NFHS: When a foul occurs "on the floor" and the throw is in going to be at a designated spot I have been instructed to waive off the shot and make the foul call at the scene, designate the spot, and to not say "on the floor".

I'm curious what is the mechanic for waiving off the shot?
I've seen vetrans keep the fist up and waive with the other hand and I've seen a two handed signal like safe in baseball, among other variations.

Also I've observed an official who keeps his fist up (for the foul signal) the whole trot to the table for until he gets to the reporting area as opposed to signaly the type of foul at the spot.

What do you do?

thanks
GTW