From what I can tell, this is used as a marketing term, and therefore refers to a specific product made by the manufacturer. Lipton, for example, has a line of "saveurs du soir," and the teas come in a variety of flavors. I would tend to think these teas would have "sleepytime" properties; but if it's a coffee, then perhaps not.

Another idea: if it is coffee, then perhaps it has chicory (often used as a coffee substitute) in it. I looked up one review for the Lipton saveurs du soir, and it listed the following ingredients:

Ingrédients :

Plantes aromatiques : coriandre, gingembre, chicorée et cannelle
Arôme
écorces d'oranges
Hibiscus.

(http://www.ciao.fr/Lipton_Saveurs_du_soir_orange_cannelle__A...

more on chicory:
The root of the chicory plant is long and thick, like the tap-root of the dandelion. When dried, roasted and ground, it makes an excellent substitute for coffee. There is no caffeine in chicory, and it produces a more 'roasted' flavour than coffee does. Many coffee producers offer blends with up to 30% chicory, which cuts down on the caffeine content of your cup.
(from coffeteaabout.com)