Symbol Quadcopter Metal Sign

About the Quadcopter design

Each corner holds a heavy ring with one short diagonal bar inside it, rounded at both ends and stopping well short of the far side of the ring, so every rotor shows a single blade rather than a spinning pair. The four arms meet in a chunky center block whose sides scoop inward between them, leaving a small round hole at the middle like a bolt head left out. All four bars lie on the diagonals, each one aimed straight back at that hole.