How to manifest? I suppose if this option is toggled on, then a good way to show it to other players would be if you profile them, a line shows up at the bottom:
Profile Redmond
Redmond is feeling mysterious and is not sharing a public profile.
Redmond has self-identified as a sight-impaired player.
Another way would be to put an asterisk after their name in the Who list. I am not sure how this would show up to other sight-impaired players.
Maybe my approach could here could be polished, with suggestions from sight-impaired players, but I am hoping such an option would alleviate some frustration (eg. asking questions about where something is, being told, 'use the map, chump', having to explain they are blind and can't use ascii, all around embarrassment, etc. ) And the sight-impaired player doesn't have to use it if they don't want to.