When you make a contract with someone, both of you sign it. If you make an agreement that only you sign, if that agreement is controlled by the other party, how do you know he hasn't or isn't going to add something to the agreement? So, you possibly don't want agreements you sign with government, when there is no other government person signing, to be like a valid contract that they hold you to. The answer is to sign it 'non-assumpsit', your signature. Or you can get away with n-a. Why? It means 'no contract' in legalease, the language of the legal system. This might be a good idea for the Amish, who don't want to get all tied up into government hidden and assumed contracts.