If you’re goal is just to make your video look more official by adding an FBI warning screen, there are tons of those screens that can be downloaded on the web via a simple Google search.
If you’re goal is to actually help protect your creation from unauthorized use by guaranteeing that all viewers are aware that it is protected material, pay careful attention to the wording of the various FBI copyright warning screens … most were made specifically for Hollywood films and all of the ones I’ve seen specifically warn viewers that unauthorized use of copyrighted material is illegal. So, if your material isn’t copyrighted, a warning about copyright infringement doesn’t seem to accomplish much.
With that said, note that copyrighting something is not really difficult at all. However, my observation has been that most content creators outside of Hollywood don’t bother … probably due to the reality that it makes no difference whatsoever unless:
[1] you catch someone using your material without your authorization
[2] they have gained enough money from use of your material to make going after them worthwhile
[3] you can afford the legal costs of pursuing a case against them