There are a couple of these listed on the e-place, from Poland. I'll take some more photos after it, and a few other assorted pieces, arrive in a couple weeks.

It looks similar in shape to one of the Russian BC3 / VSZ small transpositions. There are also similar small white porcelain insulators from Russia.

No embossing or other identifying marks.

According to Mical from Poland, this one was used for City Public Address speakers, and perhaps telephone usage. This is definitely a low voltage design, so power distribution or telegraph can be ruled out.

I saw a porcelain "twin" to this one at the YPCIC show in Enfleld CT, last month.

Apparently the Russian porcelain insulators were also used for "cable radio" in remote regions of the USSR, to provide state raduio broadcasts to areas which had no local radio stations.