These are a special case of wayfinding sign. I’ve been wondering the same thing, since some versions of the U.S. national traffic sign standard cover both outdoor traffic signs and indoor wayfinding. For example, Ohio’s standard includes any sign that the highway department might need to put up inside a rest area:
I’ve documented these signs along with the usual signs with the justification that foot traffic is a kind of traffic too. But the VA Signage Design Manual really pushes the limits, as fully a third of the signs are only for indoor use inside hospitals, and another third are for parking garages and elevators:
I’d assume these indoor signs are only of interest to the most dedicated of indoor mappers. Then again, airports have their own wayfinding systems as well, and airports tend to be some of the most thoroughly micromapped places in OSM.