Things were looking up for S.F.’s Union Square. Will the Ricky Pearsall shooting change that?

A commercial building is reflected in the window of another with a “For Lease” sign posted on Powell Street where empty commercial spaces are visible from the cable car turnaround to Union Square in San Francisco, in May. Carlos Avila Gonzalez/The ChronicleFor the average visitor, the dynamics at play in San Francisco’s Union Square are not always obvious: There’s a consensus that the city’s premier shopping district is cleaner and safer than it has been since the start of the …