That sounds reasonable, but this documentation claims that highway=traffic_sign must be omitted if we know more details about the traffic sign. One more thing for this proposal to clean up, perhaps.
That would still leave the signs that are physically and legally traffic signs in reality but that @yopaseopor wants to distinguish from traffic signs because they’re used differently than some better-known traffic signs. man_made=sign was documented in the context of a discussion about more substantial political signs, but I thought the idea was to be more generic than that.
That would certainly be the case for a route shield pavement marking. I was thinking of how some countries like the UK number ordinary road markings like centerlines and the lines that indicate parking restrictions. Globally, these markings are commonly tagged with keyword-like tags such as road_marking=solid_road_divider, but in fact it appears that traffic_sign-like values such as GB:1003A are already commonplace.