Signal Requirements are a setting you can add to your program. You can specify a minimum Signal of hackers who can submit reports to you. Once set, only hackers with a good enough Signal can submit; hackers who do not meet the requirement will be given a limited amount of trial reports, so they can still reach you should they come across a security vulnerability. You can find this in your team settings, under Signal Requirements.
(Note: You can only set Signal Requirements once your program has been reviewed)