It's a sharpie, and I speculate it may have been specially for fabric (if there is such a thing), further adding to the preservation conundrum.

But anything alcohol based (or is a substance that has molecules around the same size) would melt a sharpie really quick.

You got me thinking about this differently now, specifically about different solvents that would have been in your spray primer. Acetone is common in epoxies and primers, and it will aggressively remove sharpies as well. (Water is also a solvent, and smaller than acetone or isopropyl, but something something polar/non-polar, or something. Sharpie ink is naturally hydrophobic anyway, but not completely.) Other, equally effective solvents exist to remove sharpie and also, well, act as a solvent for other uses.

So, point being, you just eliminated what is likely to be a fairly large range of possible coating options to choose from, which is a good thing. (I completely forgot solvents are a huge thing to consider, as did a few others here.)