Ownership flag
From wipipedia.org

The Ownership Flag is intended to represent the Ownership subculture.
The stripes of the flag and the red colour of the shield were inspired by the Leather Pride Flag, with black and white chosen to represent the "cage bar" stripes of convict uniforms, and the sharp distinction between owners and owned.
The red shield and collar represent owners and owned respectively, and are part of the set of Ownership Icon symbols for different orientations and genders.
The shape of the collar also looks like a letter O for "ownership".