Since the reason for having the symbol was so that locals wouldn't fire on aircraft and vehicles, there's every reason to have it on the nose--where it hopefully gets seen before they fire--as well as on the tail, where it gets seen after they've shot.
I remember a Brit Bobby on a truck ranting, "They cant do this, they cant do this," just after his vehicle got rocketed and shot up by a few terrs who didnt bother with things like "agreed recognition symbols." We armed him after that, at his request