Residents are assuring me it’s just good advertising to suburban commuters. Here’s one e-mail:

Would that it were true. Those billboards are
advertising to the suburbanites who commute to or
through Philly. Most middle-class families (and anyone
else uninterested in politics based on race or high
taxes) have left Philly in the last decade. (I believe
Philly is the only city of America’s ten largest to
have lost population over that period.) What is left
is lots of Democrats, including a huge academic
community (UPenn, Villanova, Temple, St. Joseph’s,
Loyola).
Trust me, there is as little acceptance of
conservatives in Philly as in NYC, maybe less.