We offer Nikolas #8321 Lacquer to SLOW down tarnishing. The lacquer requires an extra day in production to dry. UV Protective lacquer is also available at your hardware store and should be reapplied every year or when needed.
We use Nikolas #8321 Clear Exterior Lacquer: a water-white, air drying, solvent based coating. It will produce a quality UV and weather resistant protective coating for brass. #8321 Clear Exterior Lacquer is particularly suited for exterior protection of non ferrous metal like brass and has excellent adhesion. Nikolas #8321 Clear Exterior Lacquer is recommended for use on exterior hardware fixtures for the boating industry, both freshwater and saltwater.
Your sign can be cleaned at any point using products like Brasso to return it to its original shine. Brass is a soft metal and small scratches may appear when polished. Try to polish with the grain of the brass and use a soft cloth.