Section 3120B.11 "Diarrhea" indicates the sign must have letters at least 1 inch high, clearly states what is noted above, and is posted at the entrance area of a public pool. Public pools include municipal/park district pools, hotel pools, water parks, swim schools, homeowner shared pools, apartment pools, campground pools, etc. One is thus not required to post this sign at your home pool (unless you really want to).
CDC ADVICE TO PREVENT INFECTIONS FROM PUBLIC SWIMMING POOLS
According to this source, the diarrhea sign and a variety of other pool signs were put into law in late 2012. Some examples of other public pool sign requirements include:
"No Diving" sign for pools with maximum depth of 6 feet or less
"No Lifeguard" sign when applicable
Emergency sign with 911 and nearest emergency services
"No use after dark" sign for pools without lighting
Artificial respiration and CPR sign
Pool user capacity sign (1 person per 10 sq ft in spa; 1 person per 20 sq ft in pool)
So you've learned something new. If you'd like to read the entire 28 pages of Chapter 31B of the California Building Code, or any of the Code for that matter, visit www.bsc.ca.gov/Codes.aspx.
DOZENS OF VENTURA COUNTY AREAS SWIMMING POOLS AND WATER PLAY PLACES