In HCM city, or Hanoi, or Guangzhou, or any major city, you need to take precautions. Slide sling is always the best, with one hand on the camera at all times, and even when slung, camera is in the front of the body. Always be on the lookout. Even when shooting, my camera never gets unslung from me.
Even during crossing bridges last nov, 2 of our members almost got robbed. Luckily both attempts failed, but resulted in one of our singaporean members injured, as he was dragged by the handstrap.
so always be on the look out, don't indulge too much in your LCD screen. Make quick checks. When you shoot, see your subject, lift up and shoot immediately, and lower. Be defensive.
Another thing is, being very friendly with the locals, vendors and all, really helps. Most of the time we were laughing together, and as I leave we always smile and wave goodbye. And more than often, these vendors remember us the next time they see us, and will smile and wave. This will make the crooks think twice, because they are not sure if these locals know us or not. ANd many times, these locals have helped some of my friends to stay out of trouble.