The big thing I just can't forgive in this movie is the flaming skull

The rest of the odd things he did make sense as a big part of Franks character is the psychological warfare, so the tombstone and the money scenes were in character even if they seem a little odd.

But trying to imagine him trying to covertly set up this big art project which would have taken hours, right next door to a lot of people who want him dead, with little cover or protection if he was discovered and for what, he doesn't even let it off till everyone's dead. By that time Saint is more worried about the fact that he's on fire than he is that there's a big flaming skull in the car yard, not that he could even tell from his perspective.

His actions would have made top story and other criminals would have taken note of one lunatic single handedly wiping out a large organised crime organisation with or without the flaming skull. It's insignificant to this. Any criminals talking about this will be talking about the death and destruction, not the skull. So who's he do this big art project for? Does he have a thing for a helicopter pilot or something?