I am really surprised by the tone of most of the comments. I don't think this is a subject to joke about, and usually boing boing readers are more sensitive. At least that is the reason why this is about the only site where I even bother reading the comments.
I think it's a great idea to have this formalized way of asking for help, because then you can be sure the staff you are talking to knows exactly what's your problem. If you fear to not make your situation clear or get a response like "c'mon, give the guy a chance, he looks rather decent", then you probably don't speak up at all. When you don't know what's in your drink when you return from the bathroom, this might be your only chance to get help.
After reading about "Ask for Angela" a few weeks ago, my first thought was "yes, but if everyone knows the code, that could be a problem". Using different signals is a good idea, although this one is maybe a tad to complicated if you are already in a stressful situation.