Can't speak for Ford, but at least with Toyota (who my employer supplies) they'd often ask for new project trial parts with QC measurements written on the parts in permanent marker (so they could see what the parts did dimensionally when welding into assembly and to be able to audit our QC reporting on said parts). I'd hear stories of people finding said marks on early production (pre-production?) Toyota vehicles when pulling interior panels.
Any more, the requirement (for body components that will be washed and painted/coated later by the/a customer) is that everything be in water soluble ink... we mark parts for reasons (can't say what/why- trade secret) and our suppliers do too, but Toyota doesn't generally care as long as it goes away by the time everything is washed. However, some parts don't get washed (such as the exhaust assemblies the other part of the company makes)... send a part with stuff written on it (especially things like "BAD") and they formally complain (DAMHIK).
1984 F150: 300 L6, AOD, RWD. EEC IV / TFI, Feedback Carter YFA Carb. Stock everything but radio (for now).