Yes, you can absolutely add a small plaque or dedication to a park bench without ruining the finish, but the right method depends on the bench material and how permanent you need it to be. I would start by checking with the park or property owner. Many public benches have rules about size, materials, and installation methods, and some parks departments will even install the plaque for you or recommend an approved approach.
For a wooden bench with a clear coat, paint, or stain, the most finish-friendly option is usually a clamp-on or edge-mounted plaque bracket. If the bench has exposed slats or armrests, you can slide or tighten a bracket into place without drilling or gluing anything to the finished surface. Just make sure the bracket is stainless steel or powder-coated aluminum so it does not rust and stain the wood.
If you prefer to attach the plaque directly, use a high-quality outdoor polyurethane adhesive or a marine-grade construction adhesive. Clean the spot with isopropyl alcohol and let it dry completely before bonding. Test on a hidden area first if you can. The downside is that strong adhesives can pull up some finishes if the plaque is ever removed, so think of this as fairly permanent.
If you must use screws, drill small pilot holes with a sharp bit, then seal the holes with exterior wood sealer or marine epoxy before and after inserting stainless steel screws. This keeps moisture from getting under the finish and causing peeling, rust, or rot. It will still leave small holes, but sealing them carefully makes a big difference.
For a powder-coated metal bench, avoid drilling if possible. A drilled hole breaks the powder coating and invites rust behind the finish. Instead, use stainless steel band clamps or U-brackets lined with a thin rubber or felt pad. These can wrap around a rail or slat without scratching the surface. If adhesive is the only option, choose a structural adhesive rated for outdoor metal and follow the cleaning instructions closely.
A few extra tips: do not use cyanoacrylate super glue or cheap double-sided tape. They tend to fail outdoors and can leave a messy residue. If you want a fully reversible option, consider a small ground-mounted plaque stake or a freestanding stone marker placed beside the bench. It can look beautiful and never touches the finish at all.
The best truly non-damaging methods are a clamp-style bracket or a ground-mounted marker. If you go with adhesive or screws, a little extra preparation and sealing will go a long way toward protecting the finish and keeping the plaque secure for years.