The guidelines of the Americans with Disabilities Act (ADA) require that identification for permanent rooms and spaces display the name of the room in raised tactile letters along with Contracted Braille (Grade 2). The raised letters must be sans serif and in all capitals. Why all capitals since it is acknowledged that mixed upper and lower case is easier to read?
The reason is simple. Tactile letters are read by touch rather than sight. The variation in word shapes that makes mixed case lettering easier to read by sight makes letters more difficult to read by touch. It has been shown that simple, unadorned letters in all caps are easier to comprehend when reading by touch.
It has also been determined that sans serif lettering is easier to read by touch than serifed letters. This explains the change in the ADA standards in the latest guidelines (2010). Formerly, “simple” serif was allowed, but no longer. No particular letterstyle is required, but the guidelines require that the letters do not deviate much from a norm regarding character width and stroke weight.