We like recycling, we like signage, therefore we love recycled signage. These businesses in New York pay homage to their on-site predecessors. Closer to home, rather than create fresh enamel diagrams when new lines appeared, London Underground riveted painted washers to the existing signs to indicate interchanges.
(Locations: Greenwich Village, Lower East Side - both New York. Underground line diagrams at London Transport Museum, Acton Depot.)