A McDonald's restaurant sign is shown in Pittsburgh on Saturday, April 23, 2022. McDonald's is reporting earnings on Thursday, July 27, 2023. (AP Photo/Gene J. Puskar) McDonald’s is grinning thanks to Grimace after a marketing campaign to celebrate the “birthday” of its big purple mascot went viral and contributed to surprisingly strong second quarter sales. Global same-store sales, or sales at stores open at least a year, rose nearly 12% in the April-June period. That handily beat Wall Street’s forecast of a 9.4% increase, according to analysts polled by FactSet. The Grimace campaign, which featured a limited-time purple milkshake, took…