You may use the capital letter height for readability guidance. The illustration below shows how much more readable the upper and lower case word is than the all caps version having the same "footprint." Both headlines have the same "footprint". Yet, the upper and lower case version is more readable than the all-caps version.
The upper case alphabet has many more straight lines and is far simpler. A well-know typography expert once stated, "capital letters are for tombstones only!"
Visual signs may consist of text, symbol, logo, a geometric figure, a photograph, or graffiti that can be viewed and understood. On the other hand, Tactile Signs need to have raised text or design that can be read by touch. Braille, raised print, and raised symbols or pictograms are all examples of Tactile Signs.
While both types of signs should meet proper color contrast requirements, the casing requirements of the letters vary.
Chapter 7 of the 2010 ADA Standards discusses this in detail. Where a tactile sign is required to identify a door, the sign shall be placed alongside the door at the “latch side”. In the case of double doors with one active leaf, the sign shall be located on the inactive leaf. For double doors with two active leaves, the sign shall be located to the right of the right-hand door. If there is no wall space at the latch side of a single door or the right side of double doors, signs shall be installed on the nearest adjacent wall