The seat reserved for need asks a visible rule to protect an often invisible condition.

A printed rule has to do its work without knowing who is standing in front of it. The seat is set aside for a need that frequently shows no external sign: pain, dizziness, fatigue, a pregnancy at eight weeks. The sign cannot verify any of that, which is precisely why it is written in general terms rather than as a test. Asking people to prove it would defeat the purpose of having it.

If someone takes that seat, assume they have a reason and let the matter end there. If you need it, you are allowed to ask, and the asking is not an imposition.