Verbal/Non Verbal Cue for speaking loudly

Hello - Just a quick bit of advice really. Hubby and I are looking for a verbal or non verbal clue for when he is talking too loudly - which he does when is is really animated. He never notices when he is doing it and misses usual cues like people stepping away from him etc.  Me saying "I'm just here" isn't working out well for either of us as you can imagine and we were wondering if any of you had this issue and or any ideas about a cue we could use?  We have thought about maybe a wink (however I look like I'm having a stroke when I try and wink!!!)  touching my mouth (but then what if I just touch my mouth lol) rubbing my ear (what if it's just itchy!?!?!)

Any help or advice appreciated!