It is the mocking finger.

At midnight, when Kaid goes to the Mosque Mahmoud, a finger will mock the plotters till they are buried in confusion.

Thou knowest the governor of the prisons--has he not need of something?
Hath he never sought favours of thee ?" "Bismillah, but a week ago!" "Then, listen, thou shepherd of the sheep--" He paused, as there came a tap at the door, and a slave entered hurriedly and addressed Nahoum.

"The effendi, Ebn Ezra Bey, whom thou didst set me to watch, he hath entered the Palace, and asks for the Effendina." Nahoum started, and his face clouded, but his eyes flashed fire.

He tossed the slave a coin.