The hairlines are on both sides of the coin. Parallel fine lines. In the pictures the run from left to right.
I see a ton of hairlines to. You got a nice coin, $40 maybe a little high but you could probably get double on eBay with the right pictures. Def do not waste your money on PCGS on this coin. The early SF mints are all well struck so pulling a PL with one is harder then most dates like the grading standards are different. Look at my 1884 O and CC in MS65PL those you can tell from a mile away to be PL. Good luck bud
Yes, I seen some gorgeous black and white looking DMPL's. Mine looks like a dull P.O.S. compared to them. Yes, I figured if I ever didn't want it or got a nicer one, ebay would be the place to unload it.
I believe hairlines are a general term used to define very fine lines on the coins surface. The word is typically used when describing the affects of wiping the coin. When proofs were shipped from the mint in cellophane, they could rub on against the coin also causing hairlines. While not a cleaning, it is a flaw. In the example in this thread, there are so many of them on both sides of the coin, it indicates to me something was wiped across the entire surface of both sides. It leads me to believe someone used a cloth to wipe off the coin, leaving fine lines behind.