The word “Shame” was spray-painted on the walls of Ms Cash’s West Perth office on Sunday.
The phrase “Tony and Peter must resign” was also written on footpaths, a reference to Peter Dutton’s role in Friday’s leadership ballot.
On Thursday Ms Cash joined fellow WA Liberal Mathias Cormann in a press conference where they withdrew their support for Malcolm Turnbull.
Ms Cash voted for Mr Dutton in both rounds of the ballot that ended Mr Turnbull’s prime ministership.
Police are appealing for anyone with information about the vandalism to Ms Cash’s office to call Crime Stoppers on 1800 333 000 or to make a report