There are a lot of signs in Graz mentioning the string A.E.I.O.U. Habsburg Emperor Frederick III used this vocals for marking his buildings while staying in Graz. The meaning of this string is still unsolved. [German]
I discovered the depicted sign at the walls of the former castle of Graz named Grazer Burg. It is placed next to the famous double spiral stairs. Later I saw the same combination of letters at a sundial in Merano.