Generally one finger means 10 bar, a clenched fist means 50 and a T (like the time-out sign) means 100, so 180 bar would be T, followed by eight fingers. The fist as a fifty bar sign is generally used to signal you are at your reserve, therefore 150 would be T followed by 5 fingers, rather than T followed by a fist. A lot of guides and instructors like divers they are leading to signal when they get to 100 bar.
Personally I prefer one handed signals. 1 - 5 is the number of fingers held vertically and 6 - 9 is the number of fingers held horizontally plus 5. Zero looks like the okay symbol but without the 3rd to 5th fingers sticking up, so you are making a zero shape with your hand. You signal single digits only, so 170 would be one finger held vertically, two horizontally and then the zero signal. This is common in tech circles as it leaves a free hand, as one could be holding a DSMB reel etc.