I once had some 4x5 film holders that had a strip of acetate or other clear material that had a number that would imprint directly to the negative.
I think it was at the closed darkslide end. I'm sure I still have them I just avoided them because I didn't want the numbers obscuring the image border.
i have a grafmatic back that had a wheel with numbers ( and i removed it ) ... it would burn the number onto the film as you said ..
i forgot about that until you mentioned it ... but seeing i never used it, i don't even know if the numbers would have been black or white