Saurer is a very old automotive firm based in Switzerland and at one time even exported trucks and buses. 

Their most famous bus model was the Saurer L4C as it was the only bus that was authorized by the Swiss authorities to be driven across the mountain roads of Alps, so much so it earned the moniker "Alpenwagen" (Alpine wagon). 

It also had large windows that allowed the sunlight to come in and also give a panoramic view of the Alps.

These buses were also used by the Swiss Postal Authority (PTT) to deliver goods & mail as well as transport people. What was most unique about these buses was its horn that was fixed in the front. It gave a unique 3-tone sound that allowed the people in the villages to know her arrival as well as caution other vehicles, especially around hair-pin bends.