Hi, I'm very happy!

Today my college received it's first grand piano, a 1916 or 1917 Hamburg Steinway Model "O" serial # 177120 that was rebuilt 22 years ago. It is a peachy keen instrument, and now we can have a real concert series, run by guess who..c'est moi, c'est moi

It's in beautiful condition, the kind lady who donated it did not play hard, so it's essentially brand new from 1983! But my question is this; at the rear of the frame, there are these numbers and a letter cast into the iron; I have never seen this before on a New York Steinway, or on a Hamburg that I can remember; never saw a Hamburg this old, though; the numbers are...
3
1063 3 5 G
They look like that: here is a bad cell phone photo I took today of this area, at the rear (farthest away from the keyboard) of the piano; anyone know what this means?
