An Appliance Store Advertises A New Dishwasher Innovation -1951
You almost have to wonder if the sign in the window was a joke, or did some unfortunate writer really make this blunder?
Automatic Butterfingers
New York: The signpainter must have been thinking of the last time he helped dry the dishes at home, when he made this sign on the window of a Staten Island appliance store. Of course it’s a dishwasher on display, not a dishmasher. (11-26-1951) credit: Acme
My guess is, is that the sign is not painted, but are sticker letters and that the person who put up the ‘m’ accidentally placed up upside down and it is in fact a ‘w’.
The item displayed in the window is not a dishwasher but a stove. Below are photographs of the James dishwasher which had a unique feature – a glass top loader which when the dishes were clean popped open when the wash was completed.

James dishwasher credit: automaticwasher.org
From what I have read, the James dishwasher actually did have a problem. It dented pots and would frequently break dishes. So maybe the person who put up the sign was writing in earnest.
To fully appreciate how quiet modern dishwashers are you have to see the James in action. As entertaining as it might be to watch your dishes being cleaned (or broken), the racket that this thing makes is incredible. Watch and listen for yourself.
Dishmasher — Look closely, these are cling-on letters on the inside of the glass, not painted on. The W is upside down. Could have been an error or someone could have changed it to make the photo.