Viacom registered the domain name, afterl.com, on May 2, 2006 and lists MTV Networks as the contact. The site is currently inactive.
Viacom then filed docs on July 14, 2006 with the USPTO to protect the word mark, After L. Unfortunately, the description of the goods & services is quite general and broad:
Entertainment services, namely television programs featuring live action, drama, comedy, animation, music, news, and general entertainment; providing online information in the field of entertainment concerning television programs.This text is just Viacom's current boilerplate legalese for any TV show.
I haven't been able to find any other information about the phrase, but I have my suspicions. I'm guessing that "After L" will be a show on MTV about the posthumous influence of Big L on Harlem and the hip-hop scene.