You are right that the company should have given you the option to sign (or not sign) before the training, not after.

Just flatly refuse to sign. If they do try making life difficult then it's a warning sign of what kind of company this is, no?

wrong. bond is one-sided i.e. you're not allowed to resign for the duration of the bond without paying some sort of monetary penalty, but the company's ability to get rid of you (whether through downsizing or managed exit or whatever) is no different from non-bonded employees.