Business Law question.

Dan-Dan Fielding ran a small store over on 5^th St. He had an issue with people stealing from his store. He had a security camera installed and then took the photos from the camera and placed the still photos of the people stealing from the store on the window in the front of the store with a sign that read: These people are wanted for shoplifting. Store will give a $10 gift certificate to anyone that gives aid in the apprehension of these thieves. About four days after the sign went up in the store, Police Captain Gabriel Mead, who was real close to retirement and was waiting for his pension to kick in, shows up at the store with four of the thieves in question to let Dan-Dan know that they had been apprehended while Captain Mead was on his day off and that Gabriel Mead would be back in an hour for his four-10$ gift certificates. Is Dan-Dan obligated to pay Captain Mead the reward?