The initials "JDR" have been scratched onto cars in South Oxhey after 21 vehicles were damaged in the past two weeks.
The bodywork of the cars was damaged between Monday, June 30 and Monday, July 14.
Police are re-appealing for information about the vehicle damage, where the initials "JDR" were engraved onto three cars.
Police sergeant Luke Mitchell said: "This type of behavior will not be tolerated in South Oxhey and we will work tirelessly to find the person responsible so the victims can see justice done.
"I would like to hear from anyone who may know who is responsible for this. We believe the offender lives locally and may have shown off about what they’ve done. They are using the tag ‘JDR’.
"Do you know who this may be? Please contact police, or alternatively give information anonymously to Crimestoppers.
"My Safer Neighbourhood Team officers have changed their shift patterns in order to conduct proactive patrols at the times it is happening and my PCSOs are carrying out street surveys in the roads affected as we suspect the offender will live near to where these crimes took place.
"If you have any information at all, please contact police."
Anyone with any information in relation to the vehicle damage is asked to contact Sergeant Mitchell or PC Dan Jones on 101 or call Crimestoppers anonymously on 0800 555 111.