Hi could it be an emblem denoting recognition and involvement in some kind of order. Shipping, navy, etc?
A white cross on a blue background, is a French civil sign, relating to merchant shipping.
According to Encyclopaedia Universalis, merchant ships had a blue ensign with a white cross, charged with the crowned shield of France, but they used to hoist the plain white ensign (allowed only for Royal vessels, by Order of 9 October 1661 and Regulation of 12 July 1670) in order to command respect.
This usurpation was generalized around 1760 and officialized by the Order of 25 March 1765 (a distinctive emblem of the ship owner was allowed).
Pierre Gay & Ivan Sache, 15 January 1999 http://flagspot.net/flags/fr~mon.html
