The photo shows a yellow sign with the message "Korsana Hayır! No To Fake Taxi! Site Taksi Yeşilköy". The joke is that the sign is promoting a real taxi service (Site Taksi Yeşilköy) while simultaneously insulting their competitors (fake taxis). This type of humor is often used in Turkish advertising, where it is common to make fun of the competition in a humorous way. The sign is a humorous way of telling people to use a genuine taxi service and avoid fake taxis.