I remembered this cool mural from our time in Philadelphia last July, chock full of captions and references to famous Philly characters and historical events and Olde City businesses. It was done by Steve ESPO Powers and located in 2nd Street.
Decoding the references for anyone interested can be found HERE (at Phillymag.com).
One of the most famous references right at the top of the wall is the key and lightning bolts, referring to Benjamin Franklin's key on his kite discovering the conductivity of electricity.
And just to show how famous this is, James Peniston created this sculpture of Ben Franklin from old keys.