What scubakat said plus, Most all airlines now charge you a special handling fee for sporting goods equipment, including scuba gear. Some charge as much as $75 additional both ways. That's ridiculous since it doesn't require any special handling, but they do it anyway. Now that being said, I've never had one to hit me with that fee and I've traveled on several that require it. But I never carry any gear in a marked bag. I had my wife's and my regs, computers, masks, and camera in my carry-on on our recent trip to Hawaii and it got searched in the Memphis airport as we passed through the metal detector. The guy who searched it had no idea what it was, except for the camera, and after I explained it to him, he said no problem and sent us on through. But he wasn't a Delta employee, he was a security guard, so that may be why I didn't get hit with Delta's $75 fee. When we came back, I had no problems at all passing through the detector in Maui.
If nothing else, I suggest that you go to an army surplus store and pick up one of the old green army bags to put your "marked" gear bag inside. That way you'll hide the "scuba gear here" markings on your gear bag. I've never lost a piece of luggage or had one broken in to (knock on wood) but I know several people that have had both happen to them. Better to be safe than sorry. I use one of the large wheeled suitcases to put all the wetsuits, BCs, duffle bags, and etc in. I use one of the small carry-on style wheeled suitcase to put my regs(regs & computers are also in a reg bag for protection), computers, masks, and camera in, that I carry on. But you have to be careful that your bags aren't to big or too heavy, else you'll hit with an oversize/over weight fee.