It follows a major data breach earlier this month where the details of about 10,000 officers and staff were mistakenly published online.

The poster was found on Thursday on Chapel Road in Dungiven.

PSNI Assistant Chief Constable Chris Todd said: "We have contacted those involved to make them aware and recognise the impact this may have on them and their families.

"The safety and welfare of all our officers and staff remains our priority, and additional security and reassurance patrols have already been implemented across Northern Ireland as part of our organisational response.

"We have commenced an investigation into this matter and I appeal to anyone with any information relating to this incident to contact police on 101.

"We are particularly keen to hear from anyone who was travelling through Dungiven last night and who has any dashcam footage."

Personal details of around 10,000 PSNI officers and staff - including their surnames and first initial, rank or grade, where they are based and the unit they work in - were mistakenly released online in response to a Freedom of Information request.

The PSNI confirmed dissident republicans have access to the list shortly after a redacted version was posted near a Sinn Fein office in west Belfast last month.

A man appeared in court in Co Antrim on 19 August charged with two terror offences relating to the data breach.

Officers and their representative organisations have spoken out in recent weeks over concerns for their safety.

An independent review of the circumstances of the data breach is to be carried out, led by City of London Police Assistant Commissioner Peter O'Doherty.

Read more:
Why the Northern Ireland police data breach is so serious
Wife of police officer says they are 'living in fear' after data breach

Several other data breaches have since emerged, including the loss of a police officer's laptop and notebook which contained details of 42 officers and members of staff after the items fell from a moving vehicle.

In a separate incident, a document containing the names of officers and staff was stolen along with a police-issue laptop from an officer's car on 6 July.