Two motor vehicles, an Audi A4 and BMW estate car, each had a tyre slashed while they were parked in Marsh Road, Tenby, last week.
The incident occurred sometime between 7 pm on Tuesday and 9 am the following day.
One of the vehicles was again damaged while parked at Newell Hill the following Thursday.
The owner is now offering a reward of £100 for information that leads to a conviction.
Anyone with any information is asked to contact Tenby police station on 842303.