The pavement pieces share a connection with another Philadelphia street mystery: the Toynbee tiles. Philadelphia 'stikman' on crosswalks in Center City (Photos: Tyler Thrasher/FOX)Stikman outside PhiladelphiaThe project is not limited to Philadelphia. He told Streets Dept that only a very small percentage of the installations were placed by a limited group of trusted helpers. Asked why he remained connected to the city, he told Streets Dept: "It’s in my blood." Toynbee tiles in Philadelphia (Market/10th St) [Photo: Tyler Thrasher/FOX]The tiles began appearing in the 1980s and have been documented in Philadelphia, other U.S. cities and parts of South America.