How do you sufficiently inform people of danger? Usually warning signs use visually strong graphical elements and bold lettering in all caps and bright colors — reds, oranges and yellows. But sometime the opposite can attract the same attention: Clean, sober and ultra -plain signage can get the idea across that the message is both important and serious, and can provide official credibility. Last week we went surfing at San Onofre Beach, an historically and culturally significant surf spot about an hour and a half south of Los Angeles. A shark had been spotted earlier in the morning and California state beach authorities planted warning lines (pictured here) along the beach. The signage certainly looks official and the design is a simple black-and-white graphical treatment with a universally understandable icon of a shark swimming below the waterline. It at a distance, a casual view of the sign doesn’t convey danger in an obvious way. If the sign hadn’t been planted precisely in front of where we had parked and camped out for the beach day, we wouldn’t have seen it at all.