re:and the hoardings you describe are sometimes
for the benefit of "Sidewalk superintendents".

i come from a long and noble line of sidewalk superintendents... that term was made immortal with the building of Rockefeller Center in NY-- the hording round the side had 'knot holes' or other small openings for passers by to see the construction site. And they made up buttons, which were given to kid that came to the site, appointing them 'sidewalk superintendents'.
I don't know how many or how often, but enough (the are now 'collectables', and NYC trivia)

the expression might have been used before that, but the story of the buttons, which was covered in the press, made the words common.


my other obsession