I'm not sure the precise details, but there's an "industrial exemption" for engineers who work for a company that makes a product. Most of the MechE's in my department do not have licenses. One colleague is pursuing hers, but mainly on the grounds of "just because I can, so why not."
I got as far as an EIT but then went back to school and changed careers.
Engineers mostly need a PE licensure if they're going to be signing off on drawings and the like for regulators. Thus PEs are pretty common in civil engineering and, I assume, structural engineering in general. But most Mech Es aren't licensed in the US even if they have degrees from accredited schools.
