The whole 'Just Bail' Idea related to something one of the guys I know from my accommodation, who once said 'let's just bail' at a party, and so it stuck, and got written on a large board and put in the window. It was then at a recent poster sale that we saw a 'keep calm' poster, and decided to change it. It was initially going to be 'Just Bail', but this would not fit with the whole idea of an odd number of lines, so the expletive got added. We are now planning on getting the poster printed up at A2 or A1 size, and put on the kitchen wall.
I believe that in the form stated it is more a metaphor for removing someone from the tender mercies of the law by posting a bond so that they don't have to sit in a cell until they are called to answer for their deeds. Of course, the financial "experts" behind the whole meltdown will never be called to answer for their deeds, so it all metaphorically falls apart. Rather like The Bailout.