My thoughts exactly, as I have some from my drafting days in school.
I'd like to see a drawing of how that was actually done.
Hi Sam
My guess is that they are lettering layout templates. If you orientate the V slots to the side (9 and 3 o'clock) that's what they look like.
That way you don't have to draw top and bottom lines and can use standard layouts. Place them on the watch, then scribe the lettering in the slots. Or scribe the lines and then embellish with lettering if you need something fancy.
Perhaps they are so thin so they can conform to the watch a bit better and be used as concave or convex templates.
My guess is that they are home made.
Cheers
Andrew
It's really quite simple and I'm embarrassed that I didn't see how obvious it is! Here's a pic.
View attachment 30756