Yes, they have a training contract. 3 years and it's pro-rated over the 3 year term. I don't remember the training bond amount. Your bond starts at the completion of line training, so you can go all the way through training up to your line check without being bonded.
As far as enforcement, it depends. If you take off and leave in the middle of the night, they basically will hold your paycheck. I do know of some guys that have had family issues, adjustment issues, etc. They worked with HR and the CP's, continually talked with them and left on good terms. They weren't held to their bonds. How hard they can actually go after you, I don't know other than withholding your paycheck.