umpire signal

[Theisey]

I've rarely have seen an NF level umpire do that. However, I do see college level umpires to that for this reason. It tells you (if you see him) that a pass was completed behind the NZ.
Therefore, if were thinking about tossing a flag for ineligibles downfield or OPI in your area of the field, than don't bother as that pass did not cross the NZ.

You still can toss it, but in the discussion the fact that the pass was completed behind the NZ will come out and the flag waved off.