Last week I was in Sevilla, Spain, and I noticed some of the taxis (but not all of them) were displaying a digit (often a 1 or 2, sometimes a 3) on their roof. The number was yellow on the front side and red on the rear side. What could these numbers mean? It wasn't the number of passengers or the number of free seats, as far as I could see.
The first taxi has a clearly visible 1, the second one was displaying a 2.
Two other two taxis seen from the rear, the nearest one showing a 1, the other one a 2 (IIRC).