Cleaning Smooth Surfaces Test an inconspicuous area of the surface with your cleaning material. Most modern signs clean quickly. I like to start my cleaning with soap and water first and then proceed to solvents. Contact vendors responsible for these devices and encourage the vendor to use more durable methods. Read the instructions on the can.
Some solvents work better if applied with a cloth.
Others must be sprayed on the damage and allowed to sit until the paint has absorbed the solvent. Some early model traffic signs use a press on lettering that can be damaged with conventional solvents. Replacement is often the best option for these signs. There are signs whose paint is removed by any cleaning or scrubbing action. One of the best examples are old California freeway signs.