mechanic question: dead ball vs. down indication

[Theisey]

While it isn't totally wrong to indicate the play is over, unless you are using the signal to start the 40 second play clock, it would be best to not give that signal at the high school level regardless of the rule code (ncaa vs nf).
What does your state association say to do?

Wait a few seconds after the play is over, keep on officiating (dead ball stuff) then slowly raise your hand to show the next down. If you have a clear first down, of course you'd be killing the clock before any of this.

Should you have a foul after the play, you'll know it's a dead ball foul from other indications, like a whistle for one rather looking around to see if someone had put his hand in the air.