If I don't know that the play is coming back, I'm going to signal the TD. Even if I see the other official's flag, I don't know for certain who the foul is on.
Then one would need to signal
on any play where a team has posession of a live ball in their opponent's endzone; regardless of whether or not one was the calling official who threw the flag for a foul on the "scoring" team. There is no way that one can ever be 100% certain that any given, non-flagrant foul, will consequently have the prescribed penalty enforced. There is always the possibility that the offended team will decline the penalty.
That being said, I am pretty confident that the percentage by which the offended team would decline said penalty would be significantly reduced if the covering official were to go ahead and signal
after the offending team "scored"; thereby notifying all interested parties that the result of the play was a Touchdown.
Now.... To those who are fortunate enough to have a supervisor
, respect his instruction
, and do it like he wants it done.