What word or phrase does your mother always say?
1849, said to be originally a hobo term (but attested in London underclass from 1851), of uncertain origin; perhaps from monk (monks and nuns take new names with their vows, and early 19c. British tramps referred to themselves as "in the monkery"). Its origins seem always to have been obscure:
Sir H. Rawlinson can decipher cuneiform, but can he tell us why "moniker"--the word has a certain Coptic or Egyptian twang--means a name painted on a trunk? ["The Saturday Review," Dec. 19, 1857]
(also moniker or monniker or monacer or monica or monaker) A person's name, nickname, alias, etc; handle: His ''monica'' was Skysail Jack/ Ricord picked up a new moniker among US narcotics agents
[1849+ British street talk; origin unknown and very broadly speculated upon; perhaps fr transference fr earlier sense, ''guinea, sovereign,'' when used by hoboes as an identifying mark; perhaps related to the facts that early 1800s British tramps referred to themselves as ''in the monkery,'' that monks and nuns take a new name when they take their vows, and that monaco means ''monk'' in Italian; perhaps, as many believe, an alteration of monogram]