That sign is in the window of 2023 Murray Ave. (map) in Squirrel Hill, in what was most recently a dentist's office. STO Express (申通快) is a Shanghai-based shipping and logistics company that has been expanding globally in the last few years, and in 2015 it opened stateside locations in: New York City; Brooklyn, NY; two locations in Flushing, NY; Edison, NJ; and Las Vegas, NV.
Nothing about a possible Pittsburgh expansion is online yet, though Squirrel Hill would make sense if the opening, in fact, happens. It is a neighborhood with a significant international population and one that borders on two universities with growing Chinese student bodies. A 2014 Brookings Institute report notes that the top origin for Pittsburgh's international students is China, with Beijing and Shanghai being the #1 and #4 cities, respectively. According to a piece in The Pitt News last fall on the growing Chinese student bodies at two universities a few miles from Squirrel Hill:
The 2,404 Chinese international students at [the University of Pittsburgh] account for more than 50 percent of the University’s total international students. In the summer and fall of 2015 alone, Carnegie Mellon University admitted 1,101 students from China.For what it's worth, that feature---as well as an article linked yesterday and two pieces by the Pittsburgh Post-Gazette's food critic Melissa McCart, "America's Next Great Chinatown Takes Root in Pittsburgh" and "The Asian influence"---cites that population growth as the impetus being more authentic, and more-authentic, Chinese restaurants in the area.
Update (9:00 pm): Yes, that's a STO Express. These photos were taken later in the day.