Wait what?
idk about you guys but I always found mixed case harder to read especially on signage. Also mixed case looks really weird and awkward when placed on a banner especially on an entranceway.
Designers usually reach for mixed-case on signage – research has shown it to be more legible, possibly because lower-case letterforms are much more varied – the ascenders and descenders mean that from afar (or in low light, or for people with low vision), words have distinctive shapes, as opposed to using all upper-case, where words are all just rectangles. (There's some research that suggests that word-shapes are recognized before letter-shapes, which is kind of neat. For example, in the screenshot in TheTigerMaster's post above, the text is blurry, but I can still tell that the signage in the rendering says "Eglinton Avenue West" from the shape of the words.)
Of course, using all upper-case, the letters are larger, and bigger type is more legible from a distance, but that can be offset to a degree by using a typeface with a larger x-height and counters (which was the reasoning behind the creation of Clearview for highway signs).