A CE337 pilot; uncertain the landing gear was down and locked; struck the runway with the rear prop while landing.

Narrative

On final I placed the gear handle in the down position and went to full flaps. I believed I had a green and locked indication. On round out the Tower advised me to check the gear. I initiated a go around. I did not hear any buzzers or any other noises or scrapes.After the go around I cycled the gear but did not get a 'locked' light. I flew by and the Tower verified the gear was down. I was still not showing a locked indication. I performed a landing with out positive lock procedure. Upon landing was told by the Tower and an observer that they heard something hit. I inspected the belly and tail of the aircraft and noticed lots of oil but no damage or scrapes. After further inspection I noticed that the rear prop did touch the runway.I checked the gear reservoir and had a mechanic verify my readings that the hydraulic reservoir was not showing any fluid on the dipstick and was dry. During my preflight it was about 3/4 up the dip stick. I checked the engine oil and both engines are at about seven quarts; the same amount as when I departed.