It's the fifth Arabic letter on Moroccan license plates, so I assume this is the reason of the Latin letter E (which is also the fifth letter). Moreover, the Latin letter W has another meaning in Morocco
I have found an official Moroccan text ("Arrêté du ministre de l'équipement et des transports n° 2711-10 du 29 septembre 2010") which says that the Latin letter E is the official correspondance of the Arabic letter و
jfz I have found an official Moroccan text ("Arrêté du ministre de l'équipement et des transports n° 2711-10 du 29 septembre 2010") which says that the Latin letter E is the official correspondance of the Arabic letter و