Call it “404 Marketing.” Burger King is launching a campaign on Digg in which failed searches on the network will produce an error message promoting the fast feeder. For instance, if a user types in a nonsense word like “byrwe,” a message will read, “No results for ‘byrwe’ were found. Looks like your search had a typo. Blame it on your tiny hands. The beefy $1 Burger King Double Cheeseburger gives tiny hands some trouble, too.” The message then provides a hypertext linkto see examples of that “trouble.” (The campaign is expected to go live later this week. It was also up briefly last week.) BK isn’t the first advertiser to sponsor error messages. Similar things have been done with actual 404 “This page cannot be found” error messages in Singapore and Brazil, and probably elsewhere. Are there any unexplored frontiers of Web advertising? Don’t say captchas. Seth Godin has thought of that.