When I was a student working weekends in an electronics emporium, I sold transfer sets by 'ALFAC' that were for direct application to PCB's for etch resist layouts and the series also included exactly what you are asking for, all manner of knob calibration marks, headphone symbols etc. These are basically a 'LETRASET' dry transfer product that may be laquered after application on panels. I think I still have some very old sets in my attic ! Well past their best by now I suspect as they will be 25 years old ! I have not seen ALFAC transfers for many years so they may well have gone the way of the Dodo
A more recent purchase of mine was a great little Brother label printer that is connected to my PC. This can take TZ laminate label tape with a width up to 24mm. I have used 'black on clear' & 'white on black' tape on some projects and it looks far better than handpainted labels. The joy is that you can print images so a symbol or scale is achievable.
Other hobbyists use inkjet paper, printed using a PC based graphics or imaging program, then either covered with 'book cover protector' or laminated in palstic using a common cold or hot laminator.
I will see if i can track down my Alfac sets
UPDATE:
I found them quickly
The ALFAC sets have survived the years well ! I am surprised if another manufacturer does not have a similar product available. I note that 'Tandy' (Radio Shack) used to sell similar as I have some examples of such as can be seen in the picture.
Thanks for reminding me about these... a nice reminiscence of my happy days in a lovely little (high quality) electronics Emporium called 'Hanneys' of Bath during the 1980's
Fraser