I have seen these line signals before, by DRI and other PSD agencies, but my question has to do with proper communication. If you are not going to be on a comm system, then why do you want to limit the diver? I am a proponent of KISS, but there are times the KISS no longer is functional.
Assuming that this is for PSD diving, then when you have divers out in zero vis, how to get your diver to go left or right? I understand the 2 tugs to change direction but what do they do to ensure that they are always going in the right direction?
Which then brings me to the question, if you are not in comms and you are sending divers out on 4 line signals, how do you confirm the diver's air pressure? Do you have them surface and hand signal or yell back their PSI every 5 minutes? If this is the case, then you not only are wasting searching time by having the diver surface and desend every 5 minutes, but you have now risked your diver to DCS by more the very nature of Boyles law and the risk of repetitive lung expansion injury.
So while I sit here and pick apart various points and issues, I do this because our team went through the very same issues. So in researching and trying to figure out a better alternative, we contacted the US Coast Guard, being that they do MORE water rescue / recovery than any other agency, we opted for the USCG signalling program. While there is more to it, the depth (no pun intended) of communication through line signals is SO much more informative.
Team Life Guard Systems, also uses and teaches these line signals.
Dive to Tender Tender to Diver
1 - Dive is OK 1 stop, face the line, tighten line
2 - Make a notation 3 - go right (diver's)
2+2+2 problem but ok, alert back up 4 - go left (diver's)
3+3+3 problem need help 2+2 Search Immediate area
4+4+4 need immediate help! 3+3 Standy By
6+6 Found Object
While initially this seems like much more, if you use proper line technique, the line signals are very easy to give and receive.
Speaking of line signals, do you physically with one hand hold onto the line or have it tethered to a harness? Because of you are holding the line, the very principle / nature hinders your search capabilities. But that is a discussion for another time.