TSA (Transportation Security Administration) has worked with several companies to develop locks that can be opened by security officers using universal master keys.
If you lock your baggage with regular locks, security officers have to cut the locks or they might have to use force to open your baggage to examine the contents.
Currently there are two main TSA approved suppliers.
Travel Sentry and
Safe Skies.
Travel Sentry Logo
Safe Skies LogoThere are different types of
TSA locks in the market. Some comes with indicator which shows you if your baggage has been opened for security check or not. The most common indicator is a tiny window on the body of the lock. It is usually showing green color. When TSA security officer unlocks your TSA lock with their master key, the indicator turns to red. After you relock the padlock with your own key or code, the indicator goes back to green.
Key Padlock - It looks just like an ordinary padlock. Often comes with 2 sets of keys.
3 Dial Combination Padlock - Instead of using keys, you create 3 digits unlock code to open the lock.
4 Dial Combination Padlock - Instead of using keys, you create 4 digits unlock code to open the lock.

Strap Lock - Baggage strap with built in TSA lock on its clip. Comes with either key lock or combination lock.

Cable Lock - It has wire cable instead of shackle. Can be locked with keys or number dials.
Word Lock - It has alphabet on dials instead of numbers. You can create a word as unlock code.(often 4 letter words)
You can see more selection in Cool Travel Gear Store.