Khatt Items Plaques will often be used outdoors, but also indoor plaques are all but a rarety.
Outdoor plaques require the use of a strong weather resistant material. Many synthetic materials are suitable to be used outdoors. So is hardwood, but like any ‘natural’ material it will require some maintenance, or the acceptance that age will show seriously.
Metal casting is a traditional way to manufacture plaques. The price of casting can be competitive since moulds can be made today by 3D print. Also the 3D print itself can be used as a plaque, but the weather resistance of most materials used in 3D print are quite limited.