You have to have the appropriate equipment (engraver, braille pen(s), raster spheres, and the software) in order to add braille to signs. There are very specific rules for where the braille must go, the size of the spheres, the spacing between the spheres, the depth of the spheres, et cetra. Virtually impossible to do without the proper setup. The lettering on the signs is required to be a certain size, specific fonts, and must be raised. There are contrast requirements as well. Any sign that requires braille also requires that sign to be ADA compliant, but not all signs require braille.
Installation of the signs is much easier, far fewer requirements.
This is a good, concise description of the stuff you need. The rotary engraver machine is used for routing letters, numbers and graphics out of adhesive backed ADA plastic sheet. The engraver also makes the holes for the Braille beads, inserted with a Braille pen. ADA graphics and Braille can be applied to acrylic, aluminum or laminates. Certain materials that do not hold Braille beads well can have the Braille reversed out by the engraver.
A good engraving machine is not cheap, and I don't think a laser engraver will work, though someone may correct me on this. I don't actually participate in the engraving at our shop. I just draw the signs to ADA specs and turn the files over to our engraving department.
We also have a photopolymer machine, but we don't use it anymore. My boss has never seemed to be able to hire a screen printer with the expertise to screen tip the graphics successfully, so we just quit using the machine rather than pay for a more skilled screen printer. Besides, the photopolymer process stinks.
I must also mention that we do a large quantity of our ADA-compliant signage by sandblasting solid surface material, such as Corian. This method does not require an engraving machine, just a plotter to cut vinyl mask and a cabinet blaster. Though sandblasting creates flat-topped Braille dots, which are non-compliant, you can easily round the tops off with a red Scotchbright pad. Of course, we cut the blanks and any windows for name inserts on the table router, but blanks could be cut on a table saw, or with a hand router and a template (maybe even stacked two or three deep for hand routing, though I've never tried it). Corners can be rounded by hand as needed.
The latest revisions to the ADA rules for signs was in 2010, and saw many changes to the requirements. No more serifed letters for example. No fat-stroked letters. Skinny strokes only. The formula is that letter strokes can be nor more than 15% of the height of the straight letters (this is easy to calculate if you work in millimeters). The requirement for height above the floor was changed for installation, too. Color contrast between graphics and background is specified. I think it is 70%. No sharp edges or corners on the blanks. Even letter spacing is specified, as well as Braille dot size and spacing, as has been mentioned.
https://www.ada.gov/2010ADAstandards_index.htm
This link is a page at the same website Johnny Best posted above, but this is the exact page you want.
The manual is pictured in the upper left corner. You can view it online or download pdf pages. The section on signage is in Chapter 7, Section 703. It's not that long and worth printing out.
Some ADA sign suppliers have also posted info that is helpful, if not always perfectly accurate. One site has posted that Helvetica Medium as acceptable, for example. It is not. I have printed out single pages from some of these sites for quick reference.
