Still pulling at the thread. So far, everything I find about this pizzeria is a mention in a Facebook group dedicated to Bajos de Argüelles; I will keep asking to see if I can get a photo of the place or its food. It had a menu that was at least eclectic, ranging from various pizzas, entrecôte à la zingara, Hungarian goulash to Neapolitan spaghetti, Wiener schnitzel, or pork knuckle with sauerkraut and mashed potatoes...

Furthermore, the absence of the prefix 91 and the use of the old postal designation "Madrid-15" indicate that this box was printed before the generalization of modern postal codes, probably between the late 70s and early 80s.