I think the strange shapes you're seeing that seem to be letters are merely irregularities in the reef surface. The white flecks are flaws in the print, possibly from dust on the negative.
Our forensic imaging specialist, Jeff Glickman, has looked at the shadow on the reef edge and does not think it's a man-made object.
I see four anomalies in the photo that might be debris.
"A" is a dark linear shape near the shore directly opposite the bow of Norwich City. It's fairly large - maybe 30 feet long.
"B" is of similar size but as linear in shape.
"C" is smaller
We're looking at all of them through perhaps a foot or two of water. The size and position of all of three suggest that the could be deck debris from the shipwreck that has been washed overboard.
"D" is more interesting. I hadn't noticed it before. It's a black dot just about halfway between the beach and the Nessie location on the reef edge (that location is obscured by the surf in this photo). The object looks to me to be maybe three feet in diameter. I don't think it's a flaw in the photo. I think it's a thing on the reef. It is similar in general appearance to the coral blocks on the reef at the bottom of the photo but its edges seem sharper. We can be quite certain that it's not from Norwich City because it's over 1,300 feet from the ship in the wrong direction. It's apparently not Nessie moved closer to shore than in the 1937 photo because this photo was taken in 1938 and when Emily Sikuli saw Nessie in 1940 it was still where it is in the 1937 photo "out where the waves break."
I'm going to ask Jeff to have a look at it.