"5000" is an old school way of saying goodbye in "da hood." At the end of Boyz 'N the Hood, Doughboy (Ice Cube) says it to Tre (Cuba Gooding, Jr.).
We started using it when Bi-Curious BJ said it at the end of a phone call one night during the v1.0 shows. We thought it was so stupid and out of touch thus making it hilarious.
While mainly used at the end of the show to say "goodbye," we will throw it back to a Heretic who ends a call with it.
5000,
Jefe