The phrase "The law is an ass" originates in Charles Dickens' Oliver Twist, when the character Mr. Bumble is informed that "the law supposes that your wife acts under your direction". Mr. Bumble replies "If the law supposes that… the law is a ass —- a idiot. If that’s the eye of the law, the law is a bachelor; and the worst I wish the law is that his eye may be opened by experience —- by experience."
Notice how he says a ass and a idiot; it may have been acceptable in his time - or it may have been a way for him to contrast the character's speech. Either way it reminds me of an early-morning walk to the railway station last week, when for a few seconds I believed I must still be dreaming as a sign on the side of the busses there read "Take a ING mortgage."
Perhaps they meant *@#!ING...?