That's a good question.
@Amadex - for a start, does the Flarum software come with a signature extension?
When/if enabled, I would propose rules along these lines:
- No more than 2 lines for general users.
- No more than 3 lines for Hosting & Service Providers.
- No Images
- Feel free to be creative but never deceptive.
- Affiliate links are fine if prefixed as affiliate links ("aff")
- If using affiliate links make it clear where they lead e.g. "My Amazon aff. link"
- Affiliate links or any links that inject/stuff cookies to other sites for financial gain are a no-go.
- Affiliate links to hosts that have a shady reputation or have been involved in scams are not allowed (NixiHost, RackNerd, EIG owned hosts etc. to name the few "jewels").