Engravings weren't covered up, but the top chrome was ground off, after which the whole top plate was re-chromed and re-engraved. New chrome filled the original engravings and was tough enough to re-engrave with a different logo like the Leica logo.
I've owned a fake Shanghai RF in the past, it was a FED-1 that was completely remodeled as a rare Chinese RF, red engravings and all. But, no slow speed button on the front, like the original Shanghai's had.
At the moment I still own one original FED-S Komandirski. It was FED's flag ship in pre-war and early war years, until the Germans destroyed the factory at Kharkow. It has a 1/1000th top speed and a FED 50/2.0 which is a perfect Summar copy with a slightly different barrel length, non-standardized and made to match the camera body. When I found the camera and lens set, it had a ground-to-brass bottom plate (getting rid of Russian engravings) and a newly chromed top plate. At which time they probably discovered they were faking a FED-S that was worth enough already into a Leica fake, and called it a day.
As a result all top engravings are gone, but it is easy to see that the top was re-chromed, the chrome color is slightly off.

FED S with FED 100/6.3 and FED 50/2.0 lenses by
buzzardkid, on Flickr
It is shown here with the 50/2.0 an uncoupled 100/6.3 and a Canon 135 finder, since I have yet to find the proper 100mm FED finder.
When the Wall fell some East-European 'buseinessmen' started faking old FED's and Zorki's into Leica's straight away, to sell them as 'valuable rare finds' in boot sales and flea markets. In the Netherlands there is a vending site that lists a new one nearly every week, lots of people can't distinguish fake from real...