Please see the photos 

Two on on piece. 

These four items are historic German local private post stamps (Privatpost) issued during the late 19th century. During this era, the German Imperial Post (Reichspost) permitted independent, municipal courier companies to compete and handle mail delivery within individual cities. 
Here is the breakdown of each specific stamp pictured:
1. Top-Left: Bremen
2. Top-Right: Hamburg
3. Bottom-Left: Leipzig
4. Bottom-Right: Berlin