I feel like the person who made this doesn't really understand the plight of a person in a wheelchair. That's a complete lack of empathy. I bet they hang out with someone in a wheelchair and ask, "why don't you just walk? You lazy or something." I know that sounds ridiculous but there are really people out there with that little of empathy. They aren't intentionally evil, but they end up doing evil things out of ignorance.
I think someone needs to either take off that sign or put some planks of wood over the stairs. I'm not saying it's a great solution, but it's better than straight up stairs. If the person in the wheelchair gets a rolling start they could make it up the plank. Maybe a car could tow them with a rope to give them that extra speed.