"In many photos, riot police wear uniforms with the English word police on them. Ambulances, too, bear the word ambulance in English. Why not use Persian words instead of their English equivalents?
Because everyone knows English. Like many capital cities, Tehran has its emergency personnel wear markings that are internationally recognizable. Street signs, too, are translated into English, and police cars are generally inscribed in both English and Persian. That makes the city more tourist-friendly without sacrificing clarity for locals. After all, the Persian word for police is the same: polise. (Persian, or Farsi, is an Indo-European language that uses an Arabic script, but people will often use Latin lettering, also known as Penglish or Fingilish, especially when typing or texting.) It's also the same word in French (police), German (polizei), Italian (polizia), Czech (policie), and many other languages. Iranian students are required to take English classes in high school. So using the English word for police actually maximizes the number of people who will understand it."