It seemed to be just the common practice of many of the South American and Central American countrys that sold off their surplus firearms in the 50's and 60's to deface the NAtional Crest marking on the arm.
No longer being property of that particular country, the Crest which means 'Property of xx' was removed.
I've read that the process was on the demand of the country where purchased from and the work done before the shipment left that country.
Makes sense if you really want to make sure it's done and not just take the Interarms rep word for it that 'We'll take care of it for you before we sell them for $28.95".

Argentine, Peru, CostaRica, many of them used to come in as surplus with the Crest ground off.
Handguns too.. The MAnnlicher from Argentina, Steyrs from Chili come to mind.

Wether the powers in those countrys wanted to avoid finger pointing from hostile neighbors in the volitile region should the arms be turned around and supplied to the crazy guys next door,,I'd imagine that could have also factored into the idea as well.
Never the most stable region of the world.