The requirement for signage at or inside the main electrical service panel comes from the Installation Standards (IS) for CPVC. This IS for CPVC is IS 20-2005 which requires identification at the electrical service panel that the building has non-metallic interior water piping.The requirement may be in the manufacturer's installation instructions for PEX piping, however, there is no language in the 2016 CPC Installation Standard for PEX specifically stating this. Please note that PEX-AL-PEX is not an approved piping system for water distribution systems within a building, and PE-AL-PE is questionable.
The body of the California Plumbing Code (CPC) does not have such language or requirements so enforcement may vary from jurisdiction to jurisdiction.
The questionable item is that the 2016 CPC revised the Appendix I (Installation Standards) to eliminate all of the Installation Standards except it added IS 31-2014, which as mentioned, is the Installation Standard for PEX, although I do not see anywhere in the standard that requires the signage. Again, the specific PEX manufacturer's installation instructions may have the requirement.
On a side note, many jurisdictions, including the City of San Jose, opted to adopt the 2013 CPC Installation Standards into their Municipal Code. Therefore, when installing CPVC in a building in the City of San Jose, a sign in or on the electrical main service panel stating that the building has non-metallic water piping is required.
