PIT Controller described a closed runway departure event when he/she failed to note that the runway was closed and released to the airport.

Narrative

I was working in the Tower and an E170 called for taxi. Although according to the ATIS we were departing Runway 28R; at that time there was an inbound to Runway 10L. For a variety of operational reasons I decided it would be advantageous to depart Runway 10C and so I taxied the aircraft to that runway. I cleared him for takeoff and he departed without incident. Shortly after that the Airport Authority called and asked if someone had just departed the center runway. At that time I realized what I did. Fortunately there were no vehicles; men or equipment on the runway. Runway 10C had been closed all night. The Controller I relieved had briefed me on that and the information had been displayed on the SAIDS. I did not input the closed runway into the AMASS but it is not clear to me at this time whether the alert would have gone off until the aircraft had started his departure roll. We also use placards in the strip bay to indicate when a runway is closed. I think the placard was up when the county vehicle came out for his field inspection but it was not up when the aircraft departed. I was awake and alert at the time of the incident. I did visually sweep the runway before the aircraft departed and I saw the electrician's trucks on the parallel taxiway. Recommendation; I understand the closure was not on the ATIS. It should have been and I should have made sure that it was. I should have made sure the placard was up. And I should have made sure that the AMASS was set to indicate a closed runway. The Airport Authority has a trailer with a lighted X which they use when they close the runways for extended periods. Even after all my oversights; if the pilot had seen a lighted X on the runway numbers that might have made a difference.