Golden tablets with the seal of the ruler that issued the pass and the seal and name of who it was issued to. About the size of your palm of solid intricately etched gold. The holder of the tablet is backed by the authority of the king to make any required purchases on credit or enter any place they deem necessary. A very powerful token indeed.
Like a Binding Oath Ring but it stops anyone under witness protection from revealing his or her true identity to anyone. I might make this into a submission one day.