newbies cannot wear a signature or Personal Text, you cannot promote referral links, you need to level up or purchase a copper membership.
You can buy a domain for $2 on Namecheap and then redirect your newly bought domain to your affiliate site, you can then put your domain name on your signature space just create a catchy phrase, the domain should be short so that people can copy easily and paste it in their browser or you can create a Youtube video that explains the platform where you want people to sign up, then redirect your domain there, it will only take you 48 hours than waiting for weeks or months to find a way to promote your platform here, just be sure that the site you're promoting is not a scam site.
you are allowed to place referral links directly in your signature, redirecting sites is a loss of a few dollars.