Signal or Not

[umpire99]

I saw this situation in a FED game yesterday. Bases loaded with one out. A line drive is hit to F4 who catches and drops the ball in what looks like it could be on the transfer. Both umpires determined that it was no catch so no signal was made. After a few seconds of everyone standing around in confusion, the defense started stepping on bases and tagging runners.

My question is how would you handle this situation with the drop? Would you not signal at all or would you give the "safe" signal to indicate no catch as is typically done on potential trap plays?