A colloquial Scotch term for a Shilling and very common in Ayrshire. Or a colloquial name in Scotland for a Guinea.
Robert Burns, in his poem The Twa Dogs (lines 55-58), says: "He ca's his coach; he ca's his horse; He draws a bonnie silken purse, As lang's my tail, whare, thro' the steeks, The yellow letter'd Geordie keeks."
See Also: White Geordie and Yellow Geordie
Source: Frey's Dictionary (American Journal of Numismatics, Vol. 50, 1916)