The BDSM "Ownership flag", as devised by Tanos for the purpose of symbolizing the ownership subculture of those who want to be owners or owned in a relationship.[1]  It includes a shield symbolizing head-of-household status, with superimposed collar symbolizing owned status (which also of course looks like an O for "ownership").
Vectorization of raster flag design.  This vector SVG version of the flag symbol was converted from version 1.002 of the Ownership flag and icons font by AnonMoos, downloadable at [2]
Flag design and original raster images by Tanos, vector conversion by AnonMoos