Ware hawk; the word to look sharp, a bye-word when a bailiff passes. Hawk also signifies a sharper, in opposition to pigeon. See Pigeon. See Ware Hawk.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Havy Cavy * HawkersNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes