I was always taught that green tape on the GEC was a no-no- and it always seemed silly to me. This wire, after all, gets connected to all the same place as all the green wires!
More to the point, when I do a service change on an old house, it can sometimes be a bit dificult to figure out just which black-fabric covered wire is the "former GEC, now water bond" wire. Sure would hate to confuse it with a, say, range conductor and heat it up!
