"signal," 1680s, "signal calling soldiers or sailors to quarters at night," earlier tap-to (1644, in order of Col. Hutchinson to garrison of Nottingham), from Dutch taptoe, from tap "faucet of a cask" (see tap (n.1)) + toe "shut." So called because police used to visit taverns in the evening to shut off the taps of casks. Transferred sense of "drumbeat" is recorded from 1755. Hence, Devil's tattoo "action of idly drumming fingers in irritation or impatience" (1803).
"pigment design in skin," 1769 (noun and verb, both first attested in writing of Capt. Cook), from a Polynesian noun (e.g. Tahitian and Samoan tatau, Marquesan tatu "puncture, mark made on skin").
"mark the skin with pigment," 1769; see tattoo (n.2). Related: Tattooed; tattooing.