I'd like to reply to Christopher Gray on a completely different note than my
previous post:

Why not graffitti?  Combining initials and address information is a
time-honored graffitti form.  Would no. 11 refer to a nearby address?  In the
subway graffitti of my youth "Taki116" combined a name and street.

My favorite graffitti in NY is the inscriptions written by 19th century
soldiers in the temple of Dendur at the Metropolitan Museum.   Just initials
and dates there, but they remind us that we aren't the first to be awed by
this building.

I guess material culture of past centuries can be comforting after all.