Green’s Dictionary of Slang

1. the male genitals.

1781		Belle’s Stratagem 3: Maas Ogul’s fille de chambre, Riggeltail, had a very grand design to ravish me of [...] my vatch, mi Lord, and de two stones dat hang to it — de seals.
1890–1904		Farmer & Henley Sl. and Its Analogues.

2. a sheep’s head and pluck, i.e. heart, liver and lungs.

1811		Lex. Balatronicum n.p.: Watch, Chain, and Seals. A sheep’s head And pluck.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1860		Hotten Dict. of Modern Sl. etc. (2nd edn) 244: WATCH AND SEALS, a sheep’s head and pluck.
1870		Hotten Sl. Dict. [as cit. 1860].
1890–1904		Farmer & Henley Sl. and Its Analogues.
1895		Crowe Aus. Sl. Dict. 93: Watch and Heals [sic], a sheep’s head and pluck.
1901		Argus (Melbourne) 20 Sept. 6/4: Yet behold the perversity of the language When the thief speaks of a watch and seals he doesn’t mean jewellery at all, but just a sheep's head and pluck.