This road sign is an example of rosette with dihedral symmetry of type D2.
Rosette with dihedral symmetry of types D2 and D6 on a house in Trieste.See also a detail.
Rosettes with dihedral symmetry of type D2 and D6 in a house in Trieste.
Two houses in Trieste: on the left we see some rosettes with dihedral symmetry of type D1 ...