In military parlance, name and number , along with rank, are the essential forms of identification. It could simply be that Tolkien envisaged the army of Mordor to be much like the British army in which he had himself served. Admittedly I can't imagine that Tolkien was entirely happy at being called
'Tolkien, John, Second Lieutenant, WO 339/34423'. In fact I'm inclined to see this as a criticism by association of the industrial military machine, although it's funny to think of Orcs having their very own Tommy Atkins.