…indicates a one-way street and shows you the direction of traffic.
Some visitors fall into the trap of thinking Einbahn is the name of the street. Sadly, you’ll have a tricky time trying to find your hotel again if you’re looking for “Einbahnstraße”, as there are hundreds of them.
Street names are usually given on signs mounted on the sides of buildings. Like this:
Two related signs to the Einbahn are, of course, the no entry sign…
…to prevent people going down the one-way street the wrong way, and the oncoming or two-way traffic sign…
…which indicates that the one-way regulation is ending and you can expect traffic to approach from the opposite direction, too.
A lot of side streets in Vienna use a one-way system to keep traffic flowing, so expect to see these signs a lot when driving around the city.