No 4 Mk1's. Possibly Pakistani origin?
The BATF&E requirement for import markings requires stamping or engraving on the "barrel, frame or receiver" the company name, city/town and state, caliber and country of manufacture. These CAN be abbreviated. The only changes that have ever been made to this requirement, (2-3 years ago I think), was for importers using engraving equipment. There is a depth requirement of 2-3mm. This is because engraving doesn't change the metal structure and if done light enough, will disappear altogether with minimal effort. An example of this is an ex-Israeli issue Hi Power Mk.III pistol that I refinished a few years ago with phosphate and Suncorite 259 paint. When I bead blasted the the frame to prepare it for Parkerizing, the import mark completely disappeared as it was barely engraved through the original paint finish! Metal hand stamps can still be used as small as 1/32". Even the slightest strike will alter the metallurgy and the markings can be raised with chemicals for tracing should someone remove the mark. This isn't the case with pantograph engraving. ATB.