You have hit the nail with the provocative hammer.

The white hood boys adopted OUR glorious Battle Flag in the
1950's to distinguish themselves from their colleagues up nawth.
They didn't start using OUR Stars and Bars until the late 70's early 80's.

Keep in mind they have carried the Stars & Stripes since the early 1900's.
Also the Charleston killer posed with the St.Andrews cross not S&B.

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