I think it's a cool idea, but the dog owners who are causing the problem won't know what it means, or will ignore it. Apparently, this has gotten a ton of attention by the media. A lot of my non-dog training friends on Facebook are sharing it. I've also heard that there is a good amount of people using the yellow ribbon.
I'm going to put this on Rory's leash, but I'm still going to be a ninja. (If you think I'm crazy for calling myself a ninja, check this out!-
CLICK) This will only be useful when I go to the park though since people just let their dogs roam here.