Does the signage have to be inside the terminal? I'm thinking that a common use for ARRIVALS would be outside on the roadways, particularly at airports like LAX
that direct cars with passengers for departing flights to the upper level and cars picking up arriving passengers to the lower level.
Another possibility might be for signs inside the terminal for INTERNATIONAL ARRIVALS. They might no be directing the arriving passengers themselves, but rather people looking to meet people arriving on international flights.