David Tepper, Carolina Panthers owner, joined the S.C. governor and Rock Hill mayor at Fountain Park, where leaders of the state legislature and cheering fans gathered for a ceremonial bill-signing and pep rally to celebrate the NFL team’s decision to build a $200 million headquarters and training center in York County. Tepper stood by McMaster’s side as the governor signed an incentives bill — at a table flanked by Panthers helmets — passed last month by the legislature.