As for what is means,
you have to use the -s option when committing:

git commit -s

The option adds a line like this to you commit message,
nothing else:

Signed-off-by: Otto Urpelainen <oturpe@iki.fi>

For more info, check the git commit docs.

As for the lack of guidance,
it is actually a Pagure feature that such lines can be required.
The configuration option for that has simply been enabled in this repository.
The proper place to complain would be the Pagure issue tracker.

I know what it does, but it's meaningless if there's nothing to sign-off on. That's what this ticket is about.

Why would I complain to Pagure that this repo enabled an optional feature?

Oh, sorry, I misunderstood.
The original report can be read in two ways:

• It is not defined what is being signed off
• It is not defined how to satisfy the sign off requirement

I read it as the second,
in which case it would be sensible to ask Pagure to include a help text.

I have always assumed that the sign off means issuing a Developer Certificate of Origin.
But you are right,
if the meaning is not spelled out somewhere,
it does not mean that,
or anything else for that matter.

Yeah, I took the meaning of Signed-off-by lines to be common knowledge, essentially what @oturpe's link lines out. I wouldn't know where to put this, though, so contributors can find it easily – AIUI there's no way to tell Pagure to link people to some part in the docs about it when it tells them there's "something wrong" with their PR.

I wouldn't know where to put this, though, so contributors can find it easily

I have seen a few projects put this in their README or their docs (iiuc bodhi
has it in its docs)

Again, it's not the meaning of Signed-off-by that's a problem, it's the meaning for this project. I can't agree to the rules of this project if this project has no rules.

Fix queued here: https://pagure.io/fork/nphilipp/fedora-infra/rpmautospec/tree/main--random-fixes-and-additions

There's a typo in this sentence:

You need to have the legally allowed to submit any contribution to this project

But otherwise looks good.

Good catch!

Fixed: https://pagure.io/fork/nphilipp/fedora-infra/rpmautospec/c/8355b525cc20a27dbe3e9af25e7c6f6ff881b55d?branch=main--random-fixes-and-additions

Commit 18bd285 fixes this issue