I don't think they are the same. Isn't a traffic sign one that says "Stop" or "Yield" and a road sign one that says "Main Street" or "Evergreen Terrace"? I guess for Danbooru purposes we don't really need to distinguish them, though.
Posted under General
I think they are being used interchangeably anyway, though. Also, although traffic_sign has a more specific meaning, I'd argue that it's also a subset of the more general road_sign.
Can we also get street_sign aliased to road_sign?