The King's Tattoo
Charles XIV John, King of Sweden 1818-1844, had a tattoo which said "Death to Kings" or "Long live the republic"
Jean Bernadotte was a military officer in the French army during the revolution. Perhaps it was during this time, perhaps through the very anti-monarchistic Club des Jacobins of Robespierre, that he got the alleged tattoo as described above. It had of course to be hidden very well later on, in particular when he in 1810 got elected heir-presumptive of the Swedish throne, and even more so when he became King of Sweden (he's the ancestor of the current royal family). In some versions the tattoo is revealed on his deathbed.
The story is amusing, not unthinkable, included in several history books, and untrue. It was coined in the comedy Le Camarade de Lit, "The Bedfellow", by Louis-Émile Vanderburch and Ferdinand Langlé. It premiered in 1833, at the Paials-Royal of all places, and was quite a success with the audience (less so with the King). The tattoo is part of the play, used for extortion:
... The ex-grenadier reminds the King that he had once tattooed his arm with gunpowder. Carried away by old associations the King pulls up his sleeve and displays the indelible imprint of a Phrygian Cap and of a revolutionary motto, which is said to have been Mort aux Rois. The disclosure of this secret is the turning-point of the piece. The King is placed in such a dilemma by this compromising discovery that, in order to save himself from the necessity of abdication, he is compelled to give his consent to the marriage of the hero and the heroine, thus bringing the curtain down upon a happy ending to the play.
Sir Dunbar Plunket Barton
Sir Dunbar and several others claim the tattoo read Mort au[x] Roi[s] or Mort aux tyrans, "Death to the king[s]/tyrants". Another suggestion with an American ring is Liberté ou la Mort, "Liberty or death". But when the tattoo is described in the play -- it is of course much too small to be visible from the stage -- it is with the text Vive la République, "Long live the Republic":
Thiébault, riant et montrant le bras du roi.
Thiébault laughs and shows the king's arm:
Le Camarade de Lit, scene X
Swedish author Staffan Skott mentions a very genuine letter with an equally ironic phrase, published in several French and English papers:
Being a republican both by principle and by conviction, I want to fight all royalists to my death.
Thanks to Tom Foley, reference librarian at the National Library of Australia, who found the play for me