Detail of several US patents, from top to bottom:
US Patent D384,987. Toy Building Element. Oct. 14, 1997.
US Patent D384,999. Toy Building Element. Dec. 9, 1997.
US Patent D384,988. Toy Building Element. Oct. 14, 1997.
US Patent D384,986. Toy Building Element. Oct. 14, 1997.