Ever notice the first and last step of each flight of stair are painted yellow? It's actually a very specific color called "safety yellow". I guess it makes it more apparent that it is the last step?
While working on my graphics for this project, I have to pick everything that goes into it- line type, line weight, paper size, paper texture, transparency etc.
The choice of font is a no-brainer, since I will just use what the subway system uses in all of their signages- HELVETICA. In fact, there is a whole documentary about this typeface:
There is also a book about it: