California Code, Harbors and Navigation Code - HNC § 683

(a) When a new or used motorized vessel is sold in California, the two carbon monoxide poisoning warning stickers developed by the Department of Boating and Waterways shall be placed on the motorized vessel. The smaller sticker shall be placed in the interior of the motorized vessel where it is immediately visible to the person operating the motorized vessel the larger sticker shall be placed facing out on the exterior of the stern or transom of the motorized vessel, unless the motorized vessel is inflatable and the sticker would not adhere to the surface of the stern.

(b) For a motorized vessel sold by a dealer, the dealer shall ensure that both warning stickers have been affixed prior to the completion of the transaction.

(c) For a motorized vessel sold by an individual, both stickers shall be included by the Department of Motor Vehicles in the new registration material provided to the new owner, and the new owner of the motorized vessel shall be notified that he or she is required to affix the smaller sticker in the interior of the motorized vessel where it is immediately visible to the operator of the motorized vessel and the larger sticker facing out on the exterior of the stern or transom of the motorized vessel, unless the motorized vessel is inflatable and the sticker would not adhere to the surface of the stern.

(d) A warning sticker already developed by the boating manufacturer may satisfy the requirements of this section if it has been approved in advance by the Department of Boating and Waterways.

(e) This section shall become operative on May 1, 2005.