The graffito was positioned in such a way that the customs officers could not overlook it on the way home.
"All border post staff are targets", the perpetrators had smeared in large white letters on a brown harbor wall.
That was in the middle of January.
Since then a lot of graffiti has been added in Larne, a small town north of Belfast.
The message is clear.
Graffiti sprayers consider anyone who helps with the control of goods that land in Northern Ireland from Great Britain as traitors.