Police Scotland has launched an investigation after pro-UK slogans and a Nazi image were scrawled across an SNP MSP’s office.
A swastika and the phrase “UK OK” were daubed on Graeme Dey’s Arbroath High Street door over the weekend.
Officers and security officials at Holyrood were notified, although there is no suggestion of any threat to the Angus South representative.
Mr Dey said: “I am very disappointed that my office has been vandalised in this way. I have reported the matter to the police and to the parliament for further investigation, and am sure that it will be dealt with accordingly.
“However, actions such as these, carried out by a tiny minority, do not change the fact that the debate we are having on Scotland’s future is a vibrant and exciting one, with packed public meetings up and down the country.
“As the First Minister recently said, the referendum debate must be a positive one abuse such as this has no role to play.”
The graffiti was discovered by an office worker.
Once Mr Dey arrived, he called police and notified the Scottish Parliament of the incident and made sure the markings were cleaned off before constituents arrived for surgery appointments.
It is understood a marker pen was used to scrawl the graffiti across the window panel of the SNP deputy whip’s blue door.
A Police Scotland spokeswoman said: “I can confirm that officers are making inquiries into a report of a vandalism at an office premises on High Street, Arbroath, which happened some time between 4.30pm on Friday and 9am on Monday.
“Inquiries are at an early stage. Anyone with any information should contact Police Scotland on 101.”
Leaders from all sides of the independence debate have been forced to condemn abuse over recent weeks. Last week a man appeared at Haddington Sheriff Court charged with making death threats against First Minister Alex Salmond.
A spokesman for the pro-UK Better Together campaign said: “All abuse and vandalism is completely unacceptable.”
A Scottish Parliament spokeswoman confirmed Holyrood officials had been contacted by Mr Dey’s office.