Valhalley of the Dolls (1) - S6-E1
Visible crew/equipment: When Chris tells Phoebe that Paige erased Piper's memory, Phoebe shouts Paige's name then walks away from Piper, and in the next shot we can see two pink T-marks taped to the floor under the table, where Paige is holding Wyatt. (00:27:05)
Chosen answer: Her agent/manager negotiated a special billing as part of her contract. It distinguishes her from the rest of the cast, probably when she became a producer on the show.
JC Fernandez