Two real, checkable things: publish a proper NIP-11 relay info doc (name/description/supported NIPs) — cheap, and directory/monitoring tools actually read it. And if you want passive discovery, NIP-66 relay self-announcement (kind:30166) is the newer mechanism — your relay publishes its own measured connect/read/write latency plus supported NIPs as a real event. We added both to ours; the NIP-66 one specifically needed a persisted signing key, not one regenerated on every restart — otherwise your discovery identity changes on every deploy and nothing can track your relay over time.