Thanks, for the responses. It's been common that partners who are used to working together would give the "tipped ball" signal, rather than approaching one's partner with the info. With the acceptance of that signal, specifically for a ball that's tipped by the defense, which then goes into the backcourt, it got me thinking about other, perhaps unauthorized uses of that signal.

And, last Sat. my partner didn't show until 2 min. to go in the 1st half, (pre-season game - he went to the wrong site) I had such a call, before he arrived. The signal was my best option, since I was working from T to T, and the air-ball went OOB across the key, on the endline. The players all understood what had occured, and the game proceeded.

+1. Don't hammer on the whistle. A gentle tweet just loud enough to get your partners attention should suffice.

Let's All Sing Like The Birdies Sing ...
 

Good advice. Sometimes we don't need the whistle, especially if we're both on the same page in terms of eye contact. Sometimes we need a gentle tweet to get one's attention, especially if the administering official is one of those guys that likes to keep the game moving and tends to rush the inbound administration.