bona fides

[…] but my note had evidently stung him, and I had a brusque message in which he said that if I wished him to believe in my “bona-fides” (whatever he may have meant by that), I would return the money which I had had during the time that I was with him at Bradfield.

1895, A[rthur] Conan Doyle, The Stark Munro Letters: […], London: Longmans, Green, and Co., →OCLC

He sat down at a table and wrote to my dictation. The gist of it was that if a man called Twisdon (I thought I had better stick to that name) turned up before June 15th he was to entreat him kindly. He said Twisdon would prove his bona fides by passing the word “Black Stone” and whistling “Annie Laurie”.

1915 August–September, John Buchan, chapter IV, in The Thirty-Nine Steps, Edinburgh; London: William Blackwood and Sons, published October 1915, →OCLC

“I have been advised that this nameless agent is in a position to establish his bona fides at any time, as he bears a number of these cards. You see, Chief Inspector, I am frank with you.”

1919, Sax Rohmer, chapter XXIV, in Dope

If any railway official, policeman, or member of the Forces on duty, requests the discontinuance of any particular form of observation or note-taking, it is clearly right to give immediate compliance, especially when it is borne in mind that public authorities now have very wide powers to hold members of the general public in custody while inquiries are being conducted as to their bona fides.

1940 July, “Notes and News: The appearance of Evil—A Warning to Railway Enthusiasts”, in Railway Magazine, page 418