First off, even those with liens can't just go and take the car in many jurisdictions (I have no idea if LA is one of them and I'm not going to look it up because it doesn't matter in this case), you still have to go to court. In your case, you don't have a security interest in the vehicle it would seem. Taking it would be grand theft auto. You don't get to commit felonies because someone owes you money. Notaries aren't lawyers and can't give legal advice. All they attest to is that the presumed identity of those signatures they are witnessing.

