Why in Arabic?
Aha! Great question!
Mona Hatoum is the artist, and she likes to point at the idea of the youth in Arab countries, who are caught between action and inaction because of the political climates in their countries. "Waiting Is Forbidden" can be taken to mean no loitering.
Is she the photographer? Where are her pieces located?
She is a Canadian-based sculptor an most of her pieces are exhibited in Canada. Interestingly the artist hired a traditional sign-maker to create the work in the same format as a traditional Cairo street sign, which often has the name of the street written in two languages.
It's part of her series called "Cairo," where she also speaks about the immigrant journey, particularly for children and teenagers who stand between two different cultures.