The Scottish flag is a white diagonal cross on a dark blue background. Also know as the Saltire it is a representation of the cross of Saint Andrew who was martyred in Greece on a diagonal crucifix. It is supposed to be one of the oldest national flags in existence as the story of it origins take us back to the ninth century.
Legend has it that in 832 AD when an army of Scottish warriors where bravely defending themselves against a Northumbrian invasion and their opponents took the upper hand and all seemed lost the Scottish King sank to his knees in prayer crying to Saint Andrew for help. As he raised his eyes towards the heavens a white cross (presumably made of clouds) appeared against the bright blue sky. Upon seeing this the king swore that if they beat the English in the battle that Saint Andrew would be proclaimed the patron of Scotland forever. The Scots of course won the battle and the Saltire has remained since that day as the national flag of the country. And so the flag reminds the Scots of the patronage of Saint Andrew and supposedly of our victory over the English.
Scotland also has another flag associated with it. The Rampant Lion or Royal Flag of Scotland.It is based on a Scottish flag that outdates Saint Andrew's, and strictly speaking is only meant to be used by the reigning monarch, in this case Elizabeth II, in relation to their status as sovereign of Scotland *. In 1934 King George V signed a decree that allows certain breaches of protocol when used as a mark of loyalty; the offices of the Secretary of State for Scotland both in London and Edinburgh fly it, and football fans are allowed to wave it at matches. These two exceptions are unique and it is still not allowed to br flown it publicly with special permission. The Lord Lyon (*) once threatened the town councillors of Cumbernauld with an Act passed in 1679 which prescribed the death penalty for mis-use of the royal arms when they flew it above the town hall.
*The Lord Lyon King of Arms is the judicial officer responsible for upholding heraldic law in Scotland.