🚀 go-pugleaf

I saw some interesting technology on a letter from the Soviet Union.  On
the envelope (it may have been an aerogram; I don't recall) there were
six templates for digits, with printed lines indicating where the penstrokes
should go.  On the back was a sample of how they wanted each digit to look
when superimposed on that template.  They're apparently called "index numbers",
but my knowledge of Russian is sufficiently rusty that I couldn't translate
the rest of the text about them.  Judging from the addresses on the envelope,
the index numbers are used both domestically and for overseas mail.

Does anyone know anything more about this?