Starting or own a window cleaning business? We're a network of window cleaners sharing advice, tips & experience. Rounds for sale & more. Join us today!
Not done one like this but I would try a de greaser give it a good scrubb with hot water and degreaser rinse with garden hose and see what it looks like
Disclaimer: I have no idea... Ok all things are worth a punt, with graffiti you sometimes get a shadow left after removing the main graffiti... Perhaps 'Graffiti Shadow Remover' maybe worth a try if you can get some....