ESTO

Source: Facebook

ESTO = Eerste Salatigasche Transport Ondememing

Translation: First Salatiga Transport Enterprises

There are 2 big garages where ESTO operated. One is now well known for the delicious "Soto" sold in the morning (soto esto*).
*note: they have moved behind langensuko (2010)

"H" is the designated number plate for Central Java. Later on Salatiga vehicles would have "H ... B" plate.

ESTO

Credit: Didot23
"Bis ESTO" was an identity of Salatiga for sometimes. Eerste Salatigasche Transport Ondememing.

Taman Sari bus station

Credit: SalatigaKita
circa 1949

Salatiga's bus station was moved from Tamansari to Blotongan, and around yr. 2000 was moved again to Tingkir area. Today, Tamansari (and along Jl. Jendral Sudirman) is the heart of Salatiga's economy comprising of a new mall and crowded shops (google map link)

I'm not sure if those are esto or "borsalino" buses.