Dave Stadt wrote
In short, Barney Fife could "request" to see your cert, and
probably
seize it (I think that's another section of Part 61; definitely if
you're intoxicated, as recent airline events have shown.).

It doesn't say you must present it immediately when Barney requests
to see
it.

Feds don't write state laws; must look to wording of law in each
state, and they must have a law on the books to able to inspect the
cert. Sample:

"...and either or both of the certificates must be presented for
inspection upon the demand of any passenger, any peace officer, or any
official, manager, or person in charge of any airport or landing
field upon which the pilot or aircraft shall land."

The consequences of failure to present valid cert varies by state.
While most states make it misdemeanor to operate w/o a certificate,
the quoted state makes violation of the above a misdemeanor also. So,
here if you're observed by police operating an aircraft, and refuse to
present the certificate immediately upon demand, you can be arrested.

Fred F.