Great question—and the answer is a little surprising. Most metal urban benches are not covered with what most people picture as paint. They are finished with a baked-on powder coating, usually a polyester or epoxy-polyester powder. That is the tough, slightly textured skin you see on armrests, slats, legs, and bolt heads.
Powder coating is a dry finishing process. Fine particles of pigment and resin are sprayed onto the metal, then the bench is baked in an oven at around 180–200°C. The powder melts, flows, and cures into a hard film. Manufacturers prefer this for street furniture because it resists chips, scratches, UV fading, moisture, and rust far better than ordinary wet paint.
If you look closely at a city bench, you can usually tell it is powder coated. The finish tends to look even, slightly pebbled like an orange peel, and it wraps around edges without drips or brush marks. In contrast, older repainted benches often show brush strokes, roller stipple, or spray-can haze.
There are different powder types. Polyester powder is the outdoor workhorse because it holds color well in sunlight. Epoxy-polyester hybrid powders are cheaper and very hard, but they can chalk or fade outdoors, so they are more common indoors or on budget hardware. Some premium benches use a zinc-rich primer or an epoxy primer under a polyester topcoat for extra corrosion protection near coastal areas. You may also see fluoropolymer or polyurethane powder on high-end architectural benches, but polyester is the usual answer.
If you are repainting a metal urban bench yourself, you do not need to set up a powder coating oven. You can get a very good result with a direct-to-metal paint system: remove rust with a wire brush or sandpaper, wipe down with solvent, apply a rust-inhibiting primer, then use an exterior-grade alkyd enamel, acrylic enamel, or two-part polyurethane paint. For small touch-ups, a good spray enamel made for metal will work, but it will not be as durable as the original powder coat.
So, the short version: that bench is almost certainly powder coated, most likely with a polyester powder. It is chosen because it survives sun, rain, salt, and thousands of people sitting on it.