Um, no one should ignore signs of anything in this industry! Complacency causes accidents and this is an industry we cannot tolerate complacency!
So to answer your question...YES it does work!
And to stay "anti-stupid" device is some what far from the mark too. What if a crew member opens Door A but forgets to disarm Door B, tottles off and goes home! Next morning catering van arrives at Door B and needs to open the door from the outside...he wasnt the idiot but he is the one who could be injured by the inflating slide, hence the need for warning signs!