Wouldn't work in Washington State, since there is no RCW authorizing open carry, it is a right, not a privilege or permission slip item. I suppose carrying a printed copy of state preemption RCW 9.41.290
RCW 9.41.290
State preemption.
The state of Washington hereby fully occupies and preempts the entire field of firearms regulation within the boundaries of the state, including the registration, licensing, possession, purchase, sale, acquisition, transfer, discharge, and transportation of firearms, or any other element relating to firearms or parts thereof, including ammunition and reloader components. Cities, towns, and counties or other municipalities may enact only those laws and ordinances relating to firearms that are specifically authorized by state law, as in RCW 9.41.300, and are consistent with this chapter. Such local ordinances shall have the same penalty as provided for by state law. Local laws and ordinances that are inconsistent with, more restrictive than, or exceed the requirements of state law shall not be enacted and are preempted and repealed, regardless of the nature of the code, charter, or home rule status of such city, town, county, or municipality.
might be helpful, but I doubt any LEO that is telling you that open carry is illegal is going to worry about a piece of paper you are holding.