DO NOT, I REPEAT DO NOT ATTEMPT TO CASH A POSTAL MONEY ORDER WITHOUT ASKING THE USPS CLERK TO VERIFY THE AUTHENTICITY.
I had a conversation with my neighbor (LEO) a while back concerning an item I had for sale on the EE. The person that was attempting to buy my item, had ignored the "USPS MO ONLY" statement in my ad, and sent me a check drawn on a CC account. I told him that I only take USPS MO because they are secure funds, and you don't have to worry about getting burned. He told me not to be over confident in the security of USPS MO's, and said that there had been quite a few fake ones going around.
Here's the good part:
He then informed me that trying to cash a fake USPS MO (presenting forged documents for payment) was a felony, and I could end up in jail. If law enforcement had a lead, they could go after the person that sent me the MO, but I could still end up being charged with "posession of forged documents"; either way somebody was going to jail. He told me that the way the law read, as long as I didn't ask for payment, I avoided a possible felony conviction. He advised that I ask the USPS clerk to verify the authenticity of the MO, and then when it was confirmed as a legitimate document, ask for payment.
I decided that it probably wasn't bad advice, and started asking for verification before cashing my MO. The last time I did, I was speaking with a different clerk than the one that I usually conduct business with, and she thought it was a very odd request and started asking me questions. The clerk that normallly waits on me came by while we were talking and told the clerk at my window that what I was doing was a very good idea as they had taken a person out in hancuffs that morning for trying to cash a fake MO.