Peace, and Hair Grease is a non-sensical or humorous way of saying goodbye. It is shortened from the previously more commonly used phrase "Love Peace and Hair Grease" that was popular throughout the 90's.
It's usage can be traced prior to the 1990's, however it was first formerly cited in print during a September 1991 interview by rapper Flavor Flav.
Other variations of the phrase has since come into the public's consciousness during the 90's such as "Love, Peace and Chicken Grease", and "Love Peace and Taco Grease".
It's been quoted in the movie 'Pest', and is also the title of several books, poems, songs, magazine articles, and television episodes, most notably the syndicated show "Girlfriends" entitled "Love Peace and Hair Grease" released March 29, 2004.
It's now a part of American pop culture. It can be seen being referenced when describing or reporting on events or media from the past. An example of this can be seen where the author uses the phrase in part for the title of his article about Soul Train's host Don Cornelius where he discusses the show 'Soul Train' as well as the host.
I will see you later, until then, Peace and Hair Grease my friend.