St Martin’s lace, n. — Green’s Dictionary of Slang

St Martin’s lace n.

also St Martin’s rings

[16C SE St Martin’s, ‘the parish of St Martin’s-le-Grand, London, formerly celebrated as the resort of dealers in imitation jewellery’ (OED)]

respectively, fake gold lace and imitation gold rings.

1589		Plaine Percival in Brand Popular Antiq. (1904) II 394/2: I doubt whether all be gold that glistereth, sith saint Martin’s rings be but copper within, though they be gilt without .
1873		Sl. Dict. 275: St. Martin’s lace imitation gold lace; stage tinsel.