Thanks very much David.

I think you almost got it. I don't think that's a HaRav with a diacritical.  But now that you got me thinking in this direction, I do think it likely is רב which is simply Mr.

And I agree that the name itself is likely Yosef: יוסף which if you look closely, you can almost see the shadow of the missing parts of those letters.

If you click on "View original" in the lower right, you get a bigger photo. But I think that's the best possible. Those inscripted letters are definitely worn out.

Louis Kessler