This one is something of a break from the norm. There was never originally supposed to be a hidden message within the world-famous logo of Cola Cola - it's just a nice, flowing handwriting logo, with a color scheme that's become iconic. Coca Cola doesn't have a monopoly on red and white though - they're also the colors of the national flag of Denmark. Just where the 'o' meets the 'l' of 'Cola,' the handwriting crosses over itself and appears to form a white cross against the red background, and so the Danes recognized their flag in it.
Coca Cola may not have intended to put the Danish flag there, but they're happy to make use of free publicity when it offers itself up. To celebrate their newly-found connection with a country that's frequently voted as the happiest on Earth, they sent teams to Copenhagen airport to welcome visitors with giant Coca-Cola themed flags which highlighted the area said to resemble the flag. Somewhat bafflingly, they didn't also provide the thirsty tourists with a bottle of Coca Cola, which would surely have made more sense.