The sign was made by someone else and stuck on top of an existing ad on the tube (the name given to the train system in London).
Occasionally people manage to stick these on, and have them go unnoticed for a good while (or it takes a while for someone to get to removing them).
Somewhat recently, someone made an ad for an illegal weed shop on the clearnet, and had those on the tube in a similar fashion for a good while before they were removed.
The sign was made by someone else and stuck on top of an existing ad on the tube (the name given to the train system in London).
Occasionally people manage to stick these on, and have them go unnoticed for a good while (or it takes a while for someone to get to removing them).
Somewhat recently, someone made an ad for an illegal weed shop on the clearnet, and had those on the tube in a similar fashion for a good while before they were removed.