Here’s an interesting security tidbit from the world of flags.
There’s a right way and a wrong way to fly the Union Jack, but only people who are intimately familiar with the symbol will even notice.
The flag does not have reflectional symmetry, due to the slight pinwheeling of St. Patrick’s cross, which is technically called the counterchange of saltires. Thus, it has a right side and a wrong side up. To fly the flag the correct way up, the broad portion of the white cross of St Andrew should be above the red band of St Patrick (and the thin white portion below) in the upper hoist canton (the corner at the top nearest to the flag-pole), giving the Scottish symbol precedence over the Irish symbol. This is expressed by the phrases wide white top and broad side up. Traditionally, flying a flag upside down is understood as a distress signal. In the case of the Union Flag, the difference is so subtle as to be easily missed by many. In the past this has been taken advantage of by the British Army. On one occasion, a British stronghold had been captured. The captured Britons were ordered to keep flying the flag so that it was not obvious that the stronghold had fallen. However, they flew it upside-down, thus alerting some sharp-eyed British reinforcements. — Wikipedia
