In 1987, Blaupunkt, a German car stereo company, ran this ad in several national magazines in the USA.
Problem: the mountains pictured in the ad had this caption: "The mountains of Europe are just one of the obstacles Blaupunkts engineers have had to overcome to improve radio reception." Reason that was a problem? The pictured mountains are the most-photographed mountains in all of North America - the Maroon Bells of Colorado.
I sent them a letter pointing out that error - and they sent me a pen set as a "token of our thanks for your alertness". An amusing part of the letter was this: "The art director at the ad agency was certainly chagrined by your discovery, as was the ad agency."