Metal signs are often used outdoors, which means regular rain, wind, sleet and/or snow can cause the sign to rust and get dirty. Signs must be regularly maintained to keep them looking their best. Cleaning old metal signs is a challenge if dirt or rust has sat for an extended period of time, but the actual process of cleaning the signs is fairly simple.
Add several drops of dish-washing soap and a gallon of warm water to a bucket. Dish-washing soap works as a degreaser, removing grease and dirt from old metal signs, and it is gentle enough not to damage the sign's paint or surface.
Apply the solution with a wet sponge, then use a soft brush to remove any grease and dirt. Avoid wire brushes, as they can scratch the metal.
Dry the sign with a soft towel. The friction from the cloth also will help to remove any remaining dirt and debris from the sign.
Mix 1 part water with 1 part white vinegar in a spray bottle. Spray any remaining stains on the sign and wipe with the towel to remove them.
Apply rust remover to a damp cloth. Scrub any rust spots on the sign with the cloth according to label instructions, to prevent stripping the old metal sign's paint. Rinse the sign to remove any remaining chemicals.