You may not be aware of this but the ADA, or Americans with Disabilities Act, actually plays a big role in how buildings as well as signage are put together. This law, which was first implemented in July of 1990, covers quite a lot of things, and these include employment, entrances and exits, pathways, and many more. This was made to help give people with disabilities an equal chance at everything people without disabilities have access to, like gainful employment, access to public establishments, and so on.
When you say that this particular law can dictate sign and building design, you are not far from the truth. It does help give people direction in terms of how things should look since there are considerations that need to be made for compliance. For example, when it comes to your building, you will need to have ramps and entrances that can accommodate wheelchairs. This means you will need to incorporate such features into your building design in order for this to be considered compliant.
The same goes for signs that are used by buildings and various companies. These need to follow very specific design standards for these to be considered compliant. When you veer away from these guidelines, you end up with great looking signs that are not considered compliant, so you end up with signs that need to be changed, lest you get penalized for it. This is why the designs of these signs are generally dictated by the ADA, if you really think about it.
There are a number of features that you need to add to your signs for these to be within the set rules by the government. These include features that make it easy for people with visual impairments to read them, such as raised characters and braille translations. Blind people cannot read this signs with their eyes, so they have to depend on their sense of touch to be able to ascertain what each sign says. The use of tactile features like these help them read these signs, thereby giving them that equal chance of reading and understanding these.
Of course, apart from these raised characters, rules like using sans serif fonts and mounting these at a height that is easy to reach is also crucial to their being read and understood properly. Sans serif fonts are chosen by the ADA as the standard font choice (any sans serif font is permissible) due to the fact that these do not have an extra artistic stroke that would make the reading of such words and letters confusing. The prescribed mounting height also makes these signs easier to reach for and to read, which is what is needed by those with visual difficulties.