Linija 8?

Back at the time, the numbers did not mean route itself, they meant the destination, so trams had different numbers in each direction. In this case, route 8 meant destination "Maksimir". In other direction it would have another number, most likely 1 (Črnomerec).

I'm not sure whether such destination numbers should be indicated in route field alongside vehicle profile or not, as it was different than standard route numbering.

Standard way of route numbering was introduced in Zagreb in 1945 after a tram line through Mihanovićeva and Vodnikova streets was built.