Vandals daubed the graffiti on the outer wall of Terenure synagogue, in the southern suburb of the Irish capital.
Gardai said officers were investigating an “alleged criminal damage incident” on Saturday.
A spokeswoman: “No arrests have been made and investigations are ongoing.”
Staff at the synagogue said they were hoping the incident was drunken vandalism rather than a targeted antisemitic attack.
“There was nothing leading up to this. It doesn’t seem to be part of a pattern so we’re hoping it’s just a drunk fool,” a worker told The Irish Times.
The graffiti has since been removed.
Last month a security guard at the synagogue was assaulted, but his attacker reportedly had mental health issues and was not targeting the place of worship specifically.
The Terenure synagogue has previously been targeted with antisemitic graffiti.
In 2005, a 40-year-old man was jailed for 20 months after being caught spray-painting a swastika near the building’s entrance. He had also vandalised two other Jewish buildings the same night.
Ireland has few specific laws to deal with hate crimes, something the country’s government has been urged to rectify.
The rarely used Prohibition of Incitement to Hatred Act has resulted in just five convictions in 30 years.
Earlier this year, justice and equality minister Charlie Flanagan said the provisions of the act would be reviewed to ensure “racism, homophobia and all forms of discrimination are not tolerated”.