Tamga are believed to have been clan signs. They take a variety of forms including one suggestive of a stylized goat, another reminiscent of a hatchet, and another with the shape of eyeglasses held vertically. Tamga may appear on rock outcroppings, boulders, or, most frequently, on standing stones. While tamga are associated most closely with the Turkic period, many scholars believe that they go back at least to the Bronze Age.