Bawds and procuresses used to wear a ring bearing the impression of a death's head in the time of Queen Elizabeth. Allusions not uncommon in plays of the period.
“Sell some of my cloaths to buy thee a death's-head, and put [it] upon thy middle finger. Your least considering bawds do so much.” —Messenger: Old Laws, iv. 1.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894