Deeply chisel it onto a large stone. Honestly. Very few other things have concrete evidence that they physically last 500 years under real-world conditions, a

Deeply chisel it onto a large stone. Honestly. Very few other things have concrete evidence that they physically last 500 years under real-world conditions, and specific technologies rarely seem to survive even 50 without such drastic changes that they're hardly equivalent any more. And large stones are so common that it's unlikely to be desirable to use it as a resource in the future.