i normally just show my DC and the time with my fingers. Just like how u show your gauge bar/psi. I wont bother buddy or DM if i still have 15-20min before DECO at depth 30m+.
When i do deep diving i will ascend each 3m when i am about to DECO +-5min.
so Point to DC and show how many time to deco.
Well i dont know what the actual universal sign but it seems that all the divers i've dive with seem
to understand my sign.