Yes—there absolutely is, and if you live in a graffiti-heavy city, there is a good chance those benches have been treated. The stuff you’re asking about is usually called an anti-graffiti coating, and it generally falls into two camps.
First, sacrificial coatings. These are often clear wax or acrylic layers applied to urban benches and other city furniture. When someone tags a bench, graffiti removal crews use hot-water pressure washing or a mild solvent. The coating releases from the surface and takes the spray paint with it. The trade-off is that they have to reapply it after every major cleaning.
Second, permanent or non-sacrificial coatings. These are typically polyurethane, fluoropolymer, or silicone-based finishes. They create a very slick, low-energy surface, so aerosol spray paint doesn’t wet out and bond the way it does on bare metal, wood, or concrete. Fresh paint can often be wiped off with a graffiti remover or solvent, and cured paint usually comes off with pressure washing. This is the kind of spray paint protection you’re most likely seeing on newer powder-coated metal benches.
Some concrete and wood benches use penetrating sealers instead. You can sometimes spot treated surfaces by their slight gloss or waxy feel, water beading, or paint that looks like it is sitting on top rather than soaking in.
The honest caveat: no coating is a magic force field. If paint bakes on for weeks, even a good anti-graffiti coating struggles. Cities usually aim for fast removal within 24 to 72 hours, and the coating itself needs periodic reapplication because UV, weather, and abrasion wear it down over time.
So if your local benches seem suspiciously easy to clean or have that slightly slick sheen, that is probably exactly why.