A variety of colors of handkerchiefs, for all of your hanky flagging needs. Tell everyone what you're looking for without telling everyone what you're looking for.
LEFT generally indicates TOP, RIGHT generally indicates BOTTOM (fewer letters in "left" fewer letters in "top," more letters in "right" more letters in "bottom" that's how you can remember it.) Switch? Wear one in each pocket or wear one on your belt between pockets.
Keep in mind there might be slight color variations between dye lots, and that your screen may not show the color exactly.