E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Napoleon Bonaparte. When Bonaparte was banished to Elba he told his friends he would return with the violets, and Corporal Violet was the favourite toast of his partisans. When he broke his parole and reached Frejus, a gang of women assembled with violets, which were freely sold. The shibboleth was, Do you like violets? If the answer given was Oui, the person was known not to be a confederate; but if the answer was Eh bien, the respondent was recognised as an adherent.