Green’s Dictionary of Slang

a large, gold pocket watch.

c.1698		B.E. Dict. Canting Crew n.p.: Warming-pan, an old fashion’d large Watch.
1725		New Canting Dict. [as cit. c.1698].
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. c.1698].
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1853		R.S. Surtees Mr Sponge’s Sporting Tour 153: Holding up a sort of pocket warming-pan, which he called a watch.
1862		E. de la Bédollière Londres et les Anglais 318/2: warming-pan, [...] grosse montre.
1873		Sl. Dict.