This second sign was about 100 yards away from the first sign, no school any where, no real evidence of a residential area, no playground, no soccer field.
It is interesting to see signs, that you think should be "universally" understood to their meaning, and the warning they are presenting. I really don't know what they mean...another one of the mysteries of traveling in the Balkans.
By the way, in case you don't know where Montenegro is, find Italy on a world map, go east across the Adriatic, it is located between Croatia and Albania on the coast. It used to also be a part of former "Yugoslavia".