I have left a job that had a training contract after 6 months (promised one thing, delivered another). They kept my last paycheck, but never came after me for the training.
I had another employer whom I had worked for, for a year, ask me to sign a promissory note for a new aircraft type that they wanted to send me to. I told them that I was trying to buy a new house, and that I would technically be required to list this as a loan on my mortgage application. I said that if I couldn't buy a house, I would have to look for work somewhere else, but if I went to the expense of buying a house, why would I leave? They sent me to school, and I left anyhow, because of the bad taste that had left with everyone when they sprung a training contract on us after having already been there.
I had another employer try to get me to sign a contract for a 135 recurrent (again, in the form of a "loan"). They sprung this on me after I had given notice at my previous job. I quit the day before going to recurrent, and they got upset. I'm sure that this employer would have tried to come after me (that's why I refused to sign).
If you sign anything, I would put (s.u.d) next to your signature. Then if they take you to court, I would explain to the judge that you were indicating that you signed under duress. Hopefully, your attorney could get the contract negated.
It has been my experience that companies that require a training contract, usually have to because they are crappy places to work. I would never stick around at a lousy job to satisfy a training contract. I would avoid signing a "training loan".