It can be found in Caldeum Bazaar, on the table at the northwestern corner of the entrance area in a lootable bag. It is only obtainable during the quest A Royal Audience. After the escape from the palace, it can no longer be looted, and therefore is easy to miss.
It reads as follows:
Attention, Subjects of Emperor Hakan II:
A trespasser has been sighted in the city sewers. Witnesses describe the suspect as a young woman in a crimson tunic. Reports indicate that she arrived in Caldeum recently along with a party of suspicious travelers. Any information leading to her immediate capture will be handsomely rewarded by His Eminence.