The San Diego Union is reporting that luggage at the cruise terminal should be unlocked. The security inspectors will not break luggage locks to inspect what is inside, so you risk having a bag miss the ship. Here is a quote from the story:
"If we have a bag that appears to need further inspection and it's locked, we will try to contact the guest," he said, adding that inspectors won't break locks to get inside. "In any case, the bag will not go on the ship until we have inspected and cleared it."