Another repost from about 5 years ago, another "mystery" insulator from Eastern Europe or former Soviet Bloc nation(s):

Original comments, and an update:

Green Russian (?) insulator, embossed with "EKO" inside of a circle.

Update 25 March 2010:

Thanks to Donald Mecklenborg, this one has been identified. It was produced in Eldapere, Estonia, during the 1920s

[IFONA CD ???] Possibly a CD 579 or 579.5(?)