A swastika was spray-painted on the stone sign in front of a Reform Temple in Ventura, California.
The swastika was discovered on Friday at Temple Beth Torah. The synagogue also is home to a Jewish pre-school and the Ventura County Jewish Council, which all are indicated on the sign.
It is not known exactly when the vandalism took place.
Police are investigating the incident as a hate crime, the synagogue told the KTLA news station.
The temple led by Rabbi Lisa Hochberg-Miller has over 300 member families, according to its website.