Book 1 Chapter XVI Paragraph 13

If there is no possibility of carrying on any such conversation (conversation with the people regarding their loyalty), he may try to gather such information by observing the talk of beggars, intoxicated and insane persons or of persons babbling in sleep, or by observing the signs made in places of pilgrimage and temples or by deciphering paintings and secret writings (chitra-gúdha-lékhya-samjñá-bhih).