wrote

Where do you keep your certificate? I have always read that if
stopped by the police on the road they have the right to "see" your
license (AOPA decal in rear window).

But you are required to have the certificate (it is not a "license")
in your possesion only when exercising the previleges of the certificate.
If you are not acting as a required crewmember under the FAR, it can
just as well be at home in the drawer.

Bob Moore
ATP CFI