Although the reference could be related to “A drug taken illegally for recreational purposes, especially marijuana or heroin,” “smear or cover with varnish or other thick liquid,” “administer drugs to (a racehorse, greyhound, or athlete) in order to inhibit or enhance sporting performance,” or “very good,” (Taken from: https://www.google.com/search?q=Grafiti&oq=Grafiti&aqs=chrome..69i57.565j0j4&sourceid=chrome&ie=UTF-8#q=dope+definition) I chose to see such expressions, less the intelligent remarks of Bansky, as those of a stupid person.
While I say this, I understand the need to help people to understand such futile expressions of self. While they are against the law, perhaps luckily there is no attribution. I do know that these individuals are found and these seemingly Anonymous tags are then associable.
I don’t want to end up posting lonely word plays indicative of disenfranchisement.
Musings 
In Barcelona we do have great graffiti artists. Last Sunday I met my photographer friend Toni Garcia, who has taken many pictures of the best graffiti ever. There are special places in the city where it is allowed. I think graffiti is sometimes pure vandalism, but others it is real great art as in here: http://digerible.com/urbano-urbano/toni-garcia-camps/
Clearly, your examples are art, but a word referring to a “Dope,” I assume as in drugs, and perhaps as in good, but I doubt it. It is as if the person relies on their reputation, which clearly has not been established and cannot be or else the person risks arrest. There is a lack of courage, the conversation of a poem in a forest alone.
Yes, I agree with you.