[stephen f. polyak]

Frankly, I think the idea of a bad plug is too easy. As said before, a bad plug alone is simple to resolve; takes about as long to do that than to "tattoo" the engine. And after the plug is fixed, then you need to remove the symbol - more work. Since guesses are being offered, I tend to think like Steve S. Indeed, if that symbol is a sign of something bad, it was probably more serious, not easily resolved. The symbol tags the plug, the plug tags the cylinder, and that leaves open rings, valves, seals, etc. All are the kind of parts that when "off", give varying degrees of measurable/noticeable poor performance, and need more time and more resources to fix. In wartime, reduced performance does not always mean unacceptable performance. So perhaps those were markers to guide future overhaul attention. Do the two markings appear on the same side of the engine? How nice if a former Luftwaffe (or Hungarian) "black man" would weigh in to this thread . . .