Manteca police Sgt. Jodie Estarziau said Tuesday that investigators were called Jan. 28 and found the vulgarities and raw meat on the ground outside the Islamic Center of Manteca, which opened in June 2013.
Muslims do not eat pork and may consider the act offensive.
The latest vandalism comes after mosque members discovered offensive language painted on the front sign of the mosque in November.
That vandal wrote "No Allah, Only God," said Mohammad ElFarra, imam of the Islamic center.
"You can tell you're dealing with someone who is ignorant and doesn't know much," he said, because Allah is the Islamic name for God. He said there have been no overt threats despite the offensive acts.
Estarziau said investigators have no leads and have asked for the FBI's help.
Gina Swankie, a spokeswoman for the FBI in Sacramento, and Nick Pacilio, a spokesman for the state's Department of Justice, both declined to comment.
