Aluminium is excellent for durability. It naturally forms an oxide coating that keeps it rust-free under normal conditions. It only corrodes under extreme conditions of acid or salt, and even then it is better than most metals.
In the past aluminium was notoriously difficult to paint. End even when it was painted the result was very matt and prone to damage. The technology for this was developed for World War 2 planes and latter applied to some vehicles and other aluminium products. It was never too popular.
Aluminium was also coloured by the anodising technique. This used the oxidized layer to the advantage of the colouring technique. The aluminium was treated with electricity, basically forming one of the terminals in a battery. This produced a thick porous layer that could be coloured. Anodized aluminium had a rather bright, colourful and futuristic look, and proved popular for cup, utensils and other small products. Anodized metal was never appropriate for vehicles or large structures.
Often creative types would forgo colouring the aluminium and use it in its natural state. Aluminium was easily cut into lettering or shapes. Company logos, lettering and signs consisted of naturally finished aluminium on a background of a different colour. This often featured on the outdoor structures of building. These signs lasted for years.
Modern aluminium signs can now feature baked on enamel paint. This is glossy and appealing, meaning aluminium signs are both durable and able to complete with the appeal of any other signs.