The signature of the second governor of Portuguese India, Afonso de Albuquerque. 
It reads: "Aº dalbuqq". Digitally traced from http://nova-acropole.pt/images/images/afonso3.jpg.

The full signature reads: Feytura e servyço de Sua Alteza, Afonso de Albuquerque (In Your Higness' service, Afonso de Albuquerque)
Own work
Crenelator