When the Churches are standing outside the museum, a workman carrying a painting passes in front of them. The painting he's carrying is Gainsborough's "Yellow Boy" one of the unknown paintings that was in Lex Luthor's collection in Foundling (1994).
The quote "All things considered, I'd rather be in Philadelphia" is originally attributed to the comedian W.C. Fields, who was originally from Philadelphia, PA. This quote is especially fitting for Clark to quote, since Superman had just returned from preventing a nuclear reactor from melting down in Philadelphia.