I have read where the U stands for inspection, I wonder if that would apply for the D U area.

There are U marks with a crown adjacent on other parts as were show in previous pic's.

1911/1912 she's a little over 100 years old, interesting.

I am going to take a small brush and very lightly brush the drgm area to see if I get a better pic of those numbers, I am worried about doing damage so it will be very lightly for sure.