This is the claim form you need to fill out, sign and date, when you report your work injury or work related illness to your employer or supervisor.  Remember, California law mandates your employer give you this form (the DWC1) within 24 hours of reporting a work related injury or illness.
The DWC1 form comes from the Division of Workers' Compensation, Department of Industrial Relations, with the state of California.  It is a very important form as it starts your work comp injury case with your local work comp appeals board.