I quote from the Lonely Planet guide: "If you're unlucky you'll stumble upon the old stone building housing the city's meat market, not a place to explore if you're even slightly squeamish". Since I'm not I went here twice (once to check the light conditions, but the market was past its prime, once to take pictures). Unfortunately a man would not let me take a picture of the wheelbarrow filled with sheep's heads, nor of the pile of heads next to it. But I managed some other shots. The Turks are not squeamish, meat is often on display in all its gore, so why not?
And by the way: the meat on these heads can be very tasty.