I didn't read the last few pages of responses, so sorry if I'm repeating anything. Since our diving here is warm water, there aren't any glove issues to deal with. With mostly tourist divers, we get mostly BAR, but some PSI divers. Since there are a number of different ways of telling pressure, I ask my divers to just give me the number of fingers for each digit. So 120 bar is 1-2-0 and 1,200 PSI is 1-2-0-0 (using a fist or "0" ) I DO ask my PSI divers to be sure to give me "all" the zeroes....the reason being, if I have a bunch of BAR divers at 100 bar (1/2 a tank) and my PSI diver only signals 100....as I've seen happen...when he REALLY has 1,000 PSI, I will think he has 1/2 a tank (100 out of 200 bar) when he really has 1/3 tank (1,000 out of 3,000 psi).
Of course, showing the SPG would eliminate this problem. However, I might have 5~7 divers with me, and with 40meter/130' visibility, they're not going to be on me like woodticks, and to bring everyone right up next to me numerous times throughout the dive would be unduly disruptive to their enjoyment of the dive. Normally, I'll check everyone's air about 10 minutes into the dive, and devote most of my SPG supervision to the heavy breathers throughout the dive.
Here are 3 examples I've seen of how "not" to communicate your air pressure to the guide: 1) had a group of divers, and one of them, shortly into the dive, gave me a pressure far, far less than I would have expected....turns out she was reading the depth gauge (40 feet) instead of the SPG...so signalled "40 bar" which is about 20% full. 2) Gave a diver the "show me your pressure" signal. She stared at her SPG a few seconds... then signalled "8-0"....but her "8" was kind of unique. Instead of 8 fingers, or 5+3, she held her hands to actually FORM an 8....like you're looking through binoculars, but with the hands vertical instead of horizontal. 3) and finally, my favorite (so far, ha ha)....diver signalled to me 180 bar, about 90% full......except we'd already been diving more than 30 minutes, so 90% full was unrealistic...80bar or 100 bar would be more likely. So, I was trying to figure out how she came up with 180.....turns out she read her COMPASS instead of her SPG. So as long as she was pointing south, she was fine.....if she turned north, she'd be down to 0, right? The best part of it was, her friend ALSO signalled 180 bar to me.
Actually, I have a "backup" signal....looks basically like you're UNscrewing a lightbulb a half turn, which essentially means "it seems you're SPG-challenged at the moment, so just turn it so I can see it."