Once is not enough. (countdown - 9!)
欢迎 huan1ying2 - literally "joyfully receive" - welcome
您 nin2 - you (as opposed to thou)
再次 zai4 ci4 - again
光临 guang1lin2 - literally "(your) valued arrival" - your presence
Western supermarkets write: "Please come again soon".
Taken at the Hengji Mall 恒基商城 in Beijing 北京. Thanks, Werner!
P.S. For all English natives: test your knowledge of German on the subtle difference between Sie and Du (you and thou).