FBI are investigating some graffiti referencing the explosion:
"Boom, fire, RIP, Gulf, Soul, ACNF."
No indication of whether is was made *before* or *after* the explosion. They might want to keep that in mind. However, ACNF, is probably going to get a little attention one way or the other.
CNN has a full story and some better photos:
http://edition.cnn.com/2009/WORLD/americas/10/23/puerto.rico.explosion/