BEAREF wroteI didn't see it, but heard the announcer say "he traveled on the inbounds pass".
What signal do YOU use for this violation?
There is no specific signal for this. Just whistle, open hand for the violation, and point the other way, just like jdw3018 suggested. You might also point to the throw-in spot. If the coach asks for an explanation, you can explain exactly what happened then. But showing the "travel" signal just seems to suggest a pivot foot was involved, which, of course, has nothing to do with the actual violation.