This is the famous Tapeball which is made of rolled up pieces of tape. These tapes were the marks of the actors so they knew where to stand and where to go to in a scene.
Tapeball is a ball of tape, the marks that the actors stand on so they know where to stand and where to go. It was created at the beginning of season 7 when Gary Boatner began collecting all the marks of the actors.
Everyone has a different color: Holly Marie Combs - arancia, arancio Alyssa Milano - rosa Rose McGowan - Blue Brian Krause - Green Dorian Gregory - Red
Right before Christmas, Tapeball was stolen. The crew got a note that detto that "The followers of the Golden Path" had taken and hidden it.