The California Highway Patrol is investigating Steve-O for breaking the law during his SeaWorld protest.
Steve-O essentially made a video confession ... giving a blow-by-blow of how he defaced a public sign on the 5 Freeway which leads to the theme park.
Caltrans was pissed ... got the CHP involved and now Steve-O could face criminal charges -- defacing public property.
Our sources say ... it's likely the case will be referred to prosecutors and Steve-O will be charged.
Steve-O tells us, "Go ahead and charge me, Sea World Sucks!"