The graffiti was left on a wall at Edmonton police station — in an area accessible only to officers and civilian staff, according to a Metropolitan Police statement.
Swastikas are ancient symbols which date back thousands of years, but are best known for their use as Nazi insignia; they continue to be used as an emblem of the far-right.
Police in the UK are banned from supporting such groups.
The swastika was discovered on February 15 and recorded as a faith hate crime.
“A thorough investigation was undertaken but no forensic opportunities were identified,” said the police statement.
Police confirmed on Monday that they have been unable to identify the culprit.
“We take all hate crime seriously and have a zero tolerance approach,” the force added.
The police watchdog, the Independent Office for Police Conduct (IOPC), said in a statement to CNN that it had not been informed of the incident.
Police forces must refer “the most serious incidents” to the IOPC. “Police forces can also refer incidents to us if they have concerns, for instance about the conduct of their officers or staff,” the IOPC added.
Far-right activity is on the rise in Britain, according to figures released by the government’s counter-extremism program in December 2018.
Data from the Home Office’s Prevent program, a central plank of Britain’s strategy to combat terrorism, showed a 36% uptick in the number of referrals of people at risk of involvement in far-right activity (1,312 people) between April 2017 and March 2018, compared with the same period the year before.
The UK’s most senior counter-terrorism police chief has also warned that the divisive atmosphere surrounding Brexit could be exploited by right-wing groups.
Neil Basu, head of the Metropolitan Police’s counter-terrorism operations, said that after the 2016 referendum there was a rise in “hate crime,” “far-right rhetoric” and “growth of (far-right) organizations like National Action.”