Many clock frames, as below, show a pattern of repeated indentations covering most of the surface of the frame. The still is from a video showing the behaviour of the clockwork which is not relevant.
I have tried to search for an explanation and hoping an AI would know received the commentary that the marks were possibly aesthetic, provided improved grip or were a manufacturing artifact. As none of these seem likely, I asked for an appropriate StackExchange forum and was suggested either "Clockmaking & Horology Stack Exchange" or "Clocks & Watches Stack Exchange", neither of which exists. This forum seems to be the closest in intent.
As I have seen this effect on clocks mostly from earlier in the 20th century, I don't believe that they are tool marks from rollers moving material around in a CNC cutter of some sort. There is also the fact that the indentations do not cover the entire surface making the clamping hypothesis unlikely.
These marks are clearly not the same as the circular overlapping polishing marks used in the finishing of exterior visible surfaces and the introduction of features this small seem unlikely to be a work hardening exercise. The look to be too regular to be hammered individually into the plates. I don't believe the process is brass-specific - this may be self-selecting from the use of these frames.
Is there any consensus on the purpose and mechanism of application of this interesting finish? Is it still in use in current processes?
Further examples showing broader adoption of the technique, but with no clear orignial source: