Green’s Dictionary of Slang

1. diamonds, precious stones in general.

1865		Leaves from Diary of Celebrated Burglar 24/2: This ‘sheeney’ landlord had a daughter, a beautiful jewess [...] the ‘sparks’ and ‘togs’ she wore would have ransomed a prince.
1882		G.A. Sala America Revisited II 133: ‘Hock my sparks,’ ‘soak my gems,’ and ‘Walker my diamonds.’ [...] American euphemisms for the act of pawning your jewellery.
1896		A. Morrison Child of the Jago (1982) 100: Him as done the sparks in from Regent Street for nine centuries o’ quids.
1908		Denton (MD) Journal 7 Mar. 3/5: ‘Tell him ye’ve brought the sparks from Misther W.’ [Ibid.] 3/6: I knew enough of thieves’ slang to know that ‘sparks’ meant diamonds or other jewels.
1925		E. Jervis 25 Years in Six Prisons 16: I talked to him of his [...] ‘prop with sparks’ (a tie-pin set with diamonds).
1939		V. Davis Gentlemen of the Broad Arrows 210: Only ‘sparkes’ and ‘red stuff’ (diamonds and gold articles).

2. (US gay) fake jewels.

1972

B. Rodgers Queens’ Vernacular 187: sparks imitation jewels.