If you deconstruct the compound word autrefois, you get "other" and "time." Close enough. It's used primarily to mean "in the olden days." So for today, two reminders in modern Paris of life in another epoch.
First, Place de la Concorde. Site of a thousand touristy photos of Paris. Statues and fountains galore, obelisk, grand buildings on the north and south, the entrance to the Jardin de Tuileries on the east and to the Champs Elysees on the west. It was where the guillotine was set up during the French Revolution and was, at that time, called Place de la Revolution. But its origins date back to the time of Louis XV who most humbly named it after himself, as this plaque reminds us.
Next, we head to the 16th arrondissement, a long skinny slice of land which caresses the city's western edge, south of Avenue de la Grande Armee. Back in the 18th century, Auteuil and Passy were but country villages, outposts between Versailles and the city. In 1860, they became part of the city itself but long before that, this marker was set in place on what is now the incredibly charming rue Berton to mark the boundary between them.