Wikipedia wants to tell me that the twin-flagged jumping spider’s name comes from those white marks on its cephalothorax, but I’d put my money on the name coming from those bright white pedipalps, which look like little flags waving around as she moves.
This glorious little twin flagged jumping spider, Anasaitis canosa, is almost invisible on her tree! The only reason I could see her was the white “flags” of her pedipalps moving around.
These little guys live all over the southeastern United States. This page has an excellent video of one waving its little flags!