Suction cups are a great way to hang signs on glass doors, windows, and other smooth non-porous surfaces. They are best suited for lightweight 10 × 7″ / 7 × 10″ and 14 × 10″ / 10 × 14″ .055″ plastic signs.
These suction cups are 7/8" in diameter with a 5/8" long hook, and have a small nub to help pull the suction cup off of the surface.