For the most part, we don't do drift decos here (in SoCal or in the NE; for many reasons: diving in shipping lanes, diving far from shore, diving in areas with floating gill nets, etc). If I shoot a bag, it's really only to indicate that I've lost the upline and am now drifting. We are set up to deal with any in-water "emergency" (either within the team or through the use of support divers, who will already be in the water on the fixed line). As Blackwood noted, usually there is only a captain on the boat. He isn't going to be able to help solve a problem occurring underwater, so we have to dive prepared to deal with what might happen in the water. If a message needed to be relayed topside, the use of support divers who can immediately ascend is going to be more useful than a colored marker.