One large 30 fl oz Panera Charged Lemonade contains 390 milligrams (mg) of caffeine. If that sounds like a lot, that’s probably because—at least by the standards of commercial beverages—it very much is. For reference, a cup of coffee typically contains somewhere in the ballpark of 90 mg. Consuming the same volume of Red Bull, 30 fl oz, would equal only 278 mg of caffeine.
Unless their dark roast coffee was listed as having 390 mg of caffeine in it, no one seeing that sign would be expecting that much caffeine.