What do these insulators have in common? The one on the left is a German telegraph insulator, it comes from a place near Zwickau, Thuringen, Germany, in the eastern part of Germany. It was used in a railway telegraph/telephone line, poles were installed in 1930's. The blue piece is a type 2 Italian telegraph insulator of the UM (Unity Modified) series, in use between the end of 19th century and the 1920's, replaced in 1920 by the 1920 series. I found it besides a road, it surfaced during construction works; along that road in the past there was a telegraph and/or telephone line. But... at a closer look the marking on the two insulators is the same! The letters incused have same style, same dimension, the marking is the same! See net photo for the detail.