GettyImages, stock photo
https://www.gettyimages.co.uk/detail/news-photo/tourist-takes-a-picture-of-a-graffito-reading-tourist-your-news-photo/829240172#/tourist-takes-a-picture-of-a-graffito-reading-tourist-your-luxury-my-picture-id829240172
GettyImages, stock photo
https://www.gettyimages.co.uk/detail/news-photo/tourist-takes-a-picture-of-a-graffito-reading-tourist-your-news-photo/829240172#/tourist-takes-a-picture-of-a-graffito-reading-tourist-your-luxury-my-picture-id829240172
I think it's an anarchist group.
https://fr.squat.net/tag/black-triangle/
https://metro.co.uk/2017/08/07/spanish-anarchists-cover-barcelona-in-anti-tourist-graffiti-6835180/