A snake with a retained shed usually exhibits some unique signs and behaviors.

1. Folds in the lateral skin. It sometimes looks "crinkly" on the sides and belly.
2. The snake will appear stiff and have trouble moving normally.
3. Breathing trouble-looks like it is taking deep breaths or trying to. It may also open its mouth during these times.
4. Time in a shed box seems to help (only because the humidity allows the skin to stretch much more easily)

If not caught and treated in time, I believe the snake can suffers organ damage from the restriction and lack of normal oxygen. So, even if the retained shed is removed the snake may not live long.

Removing a retained shed can be easy or very difficult. Placing the snake in a warm, humid shed box for 30 minutes will help. Getting the retained shed started is sometimes difficult. I start at the chin, upper lip, corner of the mouth or the cloaca/vent area. Once started you may have to continually wet the snake to keep the shed coming off. Using warm water is best. The most difficult cases may require holding the snake under running warm water. The force of the water will sometimes cause the edge to come up and make it easier to grab and remove. If the shed is started at the cloaca/vent you will have to shed the snake backward. Care should be taken when removing the eye caps.
In the most severe cases the shed only comes off in small pieces and can take hours to remove.
Retained sheds are a serious, life threatening situation and should not be taken lightly. This is especially true with snakes under 1 year old.

Prevention
This situation can be avoided in most cases if the humidity is kept in a good range (50%-60%). Using large water bowl will help increase the humidity and give the snake/s a place to soak before the shed.

Please feel free to add additional info, photos, videos, suggestion, observations and treatments.