Marker plates, which indicate the location of hydrants or valves, can be found all over Lviv. They are on just about every building that was built before WWII. The plates ensure that a hydrant or valve can be found, in case, for example, the road is covered in mud or snow.
Many of the original metal (Austrian-era) plates still exist—though some have been plastered or painted over, and, of course, others have been removed or stolen.
The three most common plates have the letter “H,” “S,” or “Z” — abbreviations for Polish words (Polish was the main official language in Austrian and interwar Galicia):
“H” stands for the Polish word “hydrant” — fire hydrant;
“S” stands for the Polish word “spust” — the valve that flushes water from the system;
“Z” stands for the Polish word “zasuwa” — the valve for stopping the flow of water (stop valve).
The little number located at the very top is the serial number. The number above the letter is the diameter of the pipe. The number to the side is the distance in meters in the appropriate direction (indicated by the arrow). And the lower number is the distance in meters of from the wall.
Some new ones have appeared too (usually made from plastic). I’ve seen plastic ones that use the old Polish abbreviations, but also new ones with the Cyrillic letters “ПГ,” which stand for the words “пожежний гідрант”—Ukrainian for fire hydrant.
Marker plates can also be found on posts and fences.
Where some plates have gone missing, occasionally one can see the letter and numbers painted directly on the building. This was either a temporary or an even older method used for marking the locations of the hydrants and valves.