Closely guarded? No. Just throw out your arms.

[Nevadaref]

Originally posted by 26 Year Gap
This seems to fall under the same category as pointing to the floor when a shooter is on the 3 point line for a shot release.

Actually, I've been told by some very good officials that this action is done to communicate to their partner in a 3-person crew that they have the shooter inside the arc. This lets the other official, C or T, know that this official has the play covered and not to signal a 3 pt goal.