This is one of my favorites, and one I recall seeing everywhere when visiting Italy at 6 yrs of age. Since there's no bar going thru it, to my mind (40 years on), I think this sign means, 'anything goes' or 'nothing prohibited.' And judging from the cars parked every which way, pedestrians & mopeds doing whatever it is they do best, well, I still believe that it's the case today. Turns out it's a version of the 'do not enter' sign - but this one, missing the cross out bar, means that it's a one way street - not going your way.
I had to look this one up again. It's a sort of 'no standing'. I say sort of, because what happens when you get a phone call and need to pull over? Whatever it is, best not to park where this is posted (except, of course, if you're a mammoth tourist bus and then you can park - engine running - all you want).

In fact, this sign is the European equivalent of this:
When I first moved to Milano, this sign always struck me as such a nice way to put things. For years, I thought it was a sign imploring the tram drivers to watch out for pedestrians, as we'd be crossing the tracks at any given point (or, if we were bike riders, we'd be caught in the tracks, falling to the point of seeing our life pass before our very eyes - always an interesting feeling to spice up your week).
It is actually a poetic way, in the land of Dante, to implore trams to 'Go Slow' or here, 'at a man's pace.' Let's just hope by that they don't mean Schumaker or Valentino Rossi.
picture frm flikr
I have no clue if this sign means, 'No Trespassing', 'No Pedestrians allowed', or 'Attenzione! pedestrians crossing'.
But, hey, it could be worse. You could find yourself trying to find a parking place in L.A. or NYC: