In the past week someone threw a brick at the building on Road 26 near Avenue 17 and posted three signs with anti-Muslim messages.
One says quote, "No temple for the god of terrorism at ground zero." Authorities believe it's a hateful reference to the proposed Islamic center in New York.
All three signs are marked with the name "American Nationalist Brotherhood." The sheriff's office had not heard of that group until now. Local Muslims say the crimes are based on ignorance.
Madera's Islamic center plans to have two people guarding the facility every night. Members have also warned other mosques across the Valley to take extra safety precautions.