Freddy wroteAs with other violations that have no specific symbol, simply point to the spot of the violation and vocalize the infraction.
Though yes, I am a plumber, I disapprove of the made-up "swirlie" signal with the finger. It's approved by toilet technicians, but not by NFHS.
Honestly don't have an issue with the signal personally. The NFHS is generally quite behind in signals that should be already in the book IMO. For instance, I imagine that a large percentage of officials were doing the kick ball signal while it was not an approved signal. It wouldn't surprise me if the same thing was true of the tip ball mechanic.