Dear Typophiles,

I'm in the middle of research about typography used on Wrocław's (Poland) trams and buses.
I'm looking for a clues about history of such typography use or just some background about history of such digit design.
Of course it can't be connected with transportation but we're close to thinking it has some functional matter.
I'll be very glad if you could help me a little with it.

Thank you very much.

Best,
Wojtek