People are s..t. That's why many of them try to hurt quokkas. Putting up a sign trying to ask them not to hurt these critters won't work. People will just tear down the signs. People only will respect force. That's why lasers, tasers, hidden machine guns, flamethrowers, poison dart guns et al are the only things that will work. Quokkas must be protected!
I think every tourist that comes to Australia be given a special booklet on how to treat and not treat natural wildlife and the severe consequences that may befall them if they digress and try to hurt the animals. A special page should be devoted to quokkas, and big red warning letters and photos showing that if one decides to try to hurt them there will be heavy monetary fines imposed on them, and possible imprisonment!