OK is these better? They added a yellow filter but I still can not tell what that one mark is. Possibly a 51 in the circle?...........
The cross member one first - odd shape, not seen before unless the writer was really off on your car. Have examples of "P/S", nothing or "B" in that location on 68 San Jose cars. One example of an "E" but its likely a spelling error again
For the other I've not seen another like it (circled something) under the paint. DSO would mean nothing to the body guys in the first half of the build before the paint so don't think that will end up true. Might just be one of those marks that was only placed on your car and none others. But sire since you've shown it here we'll see it again somewhere at a show :0
Do have a couple (1408xx range) with a later added number to the passenger side of this marks location. Have not found a connection for that one at this point but only a couple cars out of thousands of unrestored 68 SJ cars I've seen so far
............Also were the marks wax marker or paint pen?
Permanent wax markers. On the bare metal you can tell how they grew (like an old tattoo) against the metal and making the paint applied over some (ones applied before the black) not stick well - resulting often in surface rust in some areas