Unassigned in the IANA registry since 2002 — no service owns this number.
IANA's registry carries 3546 as an explicit Unassigned entry dated 2002-09. There is no registered service name, no specification, and no product that conventionally uses it. Nmap has no name for it and finds it open only rarely. Anything bound here is an application that picked an unclaimed port, so the port number carries no information about what you are talking to.
Expose with care
Judge the actual service, not the number — an unassigned port often hides an ad-hoc admin tool or a container's published port that nobody meant to publish.
$ sudo lsof -nP -iTCP:3546 -sTCP:LISTENSeen this on your network? Beige Box scans your Wi-Fi and shows every open port on every device — and its Ports tool links straight back here.
Get Beige Box →also available as JSON · Markdown
Corrections or a missing port? Reply @rimrocksystems.