Smoking pot prohibited
This is a famous Amsterdam sign saying that smoking pot is prohibited (the fine is 50 euro, which is 80 USD). These signs get stolen very often by collectors.
O and alcohol is prohibited as well.
This photo is in the Public Domain, meaning you can use it for whatever you want, commercially or not, and you can do so without attribution to the original photographer (i.c. David Silverline). This license applies.