Hi, I cannot find the pic but I have one where you can see 2 rings on the upper part of each bench, attached to the "steel arm" that links the bech and the chopper's belly. The operators would secure their "pigtails" (kind of elastic rope with a climbing hook? at the end) to the rings during the flight and would unhook them in proximity of the LZ, as Avus said.
take care,
Seaking