Well, a dream sign is basically just a recurring situation, person, or instance that appears in your dreams. So when it happens in real life you remember to do a reality check. As you aren't actually blind in real life, it is a little harder to make the habit of reality checks sink it, but it is possible and I have actually done it with more than one dream sign. Just make a note or habit to do a reality check every time you can't see and that should carry into your dreams. If it does, then yes you should become lucid in your dream which will give you the chance to hopefully remove the blindness.