American elevator panel
"The bathroom on the first floor isn't working," I told the superintendent.
"Oh, don't worry," he said. "Just go to the one on the second floor."
We were talking about the same floor. I have been in France so long, I sometimes forget that Americans call the ground floor the first floor. In much of the rest of the world, the ground floor has a different name (in France, it's the rez-de-chaussée or level-with-the-sidewalk floor) and the first floor means what Americans call the second floor.
RC is for rez-de-chaussée and SS for sous-sol (basement). Usually 0 is a substitute for RC so I'm not clear on why they are both on this panel.
British elevator panel: G for Ground
In Chinese the words "four" and "death" sound alike, so buildings are often "missing" their fourth and fourteenth floor. For good measure, the builders also take into account the Western superstition about 13.