Poste Maurice Cortier was a desert halt in the Sahara Desert in southern Algeria. It can be found along the way from Algiers to the French Sudan.
It became popularly known as Bidon 5 because its sign board was an empty gas-can with the numeral 5 painted upon it; and bidon is French for "gas-can".
References
Poste Maurice Cortier Wikipedia(Text) CC BY-SA