EXIT signs wherever the exit path is unclear. Certainly along the path.
Life Safety 101 is available for read-only at NFPA.org "Means of Egress Marking" is the term used. See chapters 7 and A.7 for major provisions. Other references are scattered.
Your local/state Fire Chief/Marshal is often the Authority Having Jurisdiction (AHJ) on this matter as well as wiring in fire escape stairs, emergency lighting, and fire alarm systems (topics concerning electricians).
Some places do not adopt NFPA 101 and use building code provisions, I think.
You'll have them at an exit and at an entrance to an exit.
Depending on your occupancy classification and building arrangement, it can get subjective. They may or may not have to be illuminated (if an EM light shines on them you can get away with a placard sometimes).