Be very careful with taking legal advice off the internet. I'm sure the laws vary based on what state the training contract and promissary note are signed in. If you need to ask, ask an attorney in the state you're signing in.
Keep in mind that there may be other issues. The cost to defend yourself may end up costing you more than the note itself. How will your new employer feel when DPJ comes asking to help collect the debt? My company has used promissary notes and reportedly has had great sucess in collecting. There's nothing like being called out of new hire ground school to take a phone call from your previous employer. With PRIA, they'll know where you are going.