I'm offering a unique vintage padlock that reads "Street Letter Box Lock - United States - SR". This lock comes with an operating key as well. Lock is in good mechanical condition and key works. The unusual operation of this lock consists of inserting key, pushing upwards into lock, which then releases shackle. - eBay
I have no clue about the codes on the locks other than they are for the opening key. My understanding is that the code MV is for those locks that were used on vehicles.
This great-looking mail lock sold for $79.78 (Plus $7 Shipping).