At first glance, it looks like a mistake, something to be erased, or maybe a spot of dirt that’s landed on the page. Nope. It’s a diacritical mark and it indicates that the pronunciation of a letter has been modified. In the case of a cedilla (“suh-dee-luh”), most often used with words of French and Portuguese origins, the little tail or hook under a c calls for a soft c sound. Façade, for example, is pronounced “fuh-sod,” not “fuh-kod” or “fuh-kayd” (which brings out the nine-year-old boy in me and makes me giggle).
Garner’s Modern American Usage states diacritical marks “…often fall into disuse as terms are fully naturalized.” You’ll certainly see façade, Niçoise (a yummy salad), Provençal (referring to the region in France famous for gorgeous table linens and lush vineyards), garçon (a pretentious term for calling a waiter), and cachaça (a sugary liquor produced in Brazil) used in copy with just a regular ol’ c. But if your targeted audience is well-educated, well-traveled, and/or well-read, employing the cedilla will make you look smart and savvy.