In a 1964 U.S. Supreme Court case involving a movie-theater owner convicted of an Ohio law banning the showing of obscene movies, Justice Potter Stewart famously said he could not "intelligibly" define obscenity, "but I know it when I see it." People still use that line to showcase the imprecision and irrationality of many laws. How do we convict someone of something so hard to define? We often know when we see other absurdities, writes Steven Greehnut, including an archaic statute now subject of a gun-related lawsuit filed this month in federal court. California Penal Code 26820 bans gun stores from displaying signs — visible from outside the premises — picturing handguns. They aren't allowed to display words-only signs that advertise the sales of handguns, either.