Bromide compounds, especially potassium bromide, were frequently used as sedatives in the 19th and early 20th century. This gave the word "bromide" its colloquial connotation of a boring cliché, a bit of conventional wisdom overused as a sedative.
One can test for a bromide ion by adding dilute nitric acid (HNO3), then silver nitrate (AgNO3). A cream precipitate forms that disappears in concentrated ammonia solution.
Bromide is present in typical seawater (35 PSU) with a concentration of aroud 65 mg/l, which is around 0.2% of all dissolved salts.