Will a sharpie marker stay on a metal sign outside or will it wash away ?
Kathy...I really am not sure but would be afraid it would wash away. Could you use a brush and outline what you want to paint or use a stencil?
It will fade away eventually. You might be able to clear coat it with a UV stable exterior urethane.
It will fade over time especially if it is in an area where it gets backed daily by hot sun. I don't think it will "wash" off but I could be wrong.
It will fade over time. You can seal it with exterior polyurethane or a marine varnish.
Have someone make you permanent vinyl letters and apply those.