The story
Uncertain; it may have come from a resemblance to the coat of arms of Dalrymple, Lord Stair, who was an object of criticism for his part in the Massacre of Glencoe in 1692, and his work in bringing about the Union with England in 1707 (ref. Oxford English Dictionary, 2nd edition 1989).
Etymology from Wiktionary, CC BY-SA 4.0.