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.