To me, (as a white male, whose been a rep to an Alpha Phi Omega chapter at an NPHC) the major difference between the NPHC and "traditional" (1980s?) NPC signs is that NPHC signs are mostly "thrown", single hand and often with motion. traditional NPC signs are often static, involve both hands (or in some cases arms) and/or have multiple women making pieces of the sign to "assemble" one sign...
And yes, the ASL sign for Vagina is two hands making "L" signs with the index finger pointing out and down tapping together. The ASL sign for kite (which may be what they are trying to make) is one hand with a finger pointing up (as the string) toward another flat hand (as the kite) with the kite hand fluttering and the two hands move in concert up and down
Vagina:
https://www.youtube.com/watch?v=m36jIkkmezg
Kite:
https://www.youtube.com/watch?v=-nYGf9fvzk0