Eight separate incidents of cars being damaged or having items stolen have been reported in less than a week.
The first was a grey Hyundai having its rear passenger window smashed in Temple Mead, between 8pm on October 28, and 9am the following day.
Another window was smashed, on a silver Ford Focus, between 5.30pm on September 30 , and 8.10am on October 2 in The Chase.
Between midnight on October 1, and 11.55am the following day in The Chase, offenders smashed the window of a blue Vauxhall Meriva and stole a scratchcard.
A sat nav was taken when a window was broken of a blue Ford Fiesta between 10pm on September 30 and 1.15pm on October 1.
There were two more window smashes - a white Ford van in Sunnyhill Road between 3pm on September 30 and 11am on October 2, and a silver Vauxhall Golf in Barnacres Road at 4.30pm on October 2.
And also on October 2, the window of a Citroen Saxo was smashed in The Holt, between 12.40-9.15am in The Holt.
Call Herts Police on 101.