Vandals threw a bag of tar over a car which Standlake residents had strategically parked on a road to slow down speeding motorists.
The incident is the latest in a series of problems in Downs Road and nearby Church Mill Close following the closure of the A415 Abingdon Road.
Residents are concerned about the volume and speed of diverted traffic in the village since the A-road -- which links Witney with Abingdon -- closed for sewer repairs last month.
Joy Livingstone, of Church Mill Close, said her daughter Madeline had deliberately parked her white Metro on the road with a flashing orange light inside as a traffic calming measure.
But she was amazed to find somebody had thrown a bag of tar on to the car windscreen on Thursday. Mrs Livingstone said: "It's not in the spirit of goodwill at Christmas. It will be really hard to get off and the bodywork will be damaged."
A Thames Valley Police spokesman said they were investigating the attack. Anne Cullinan, whose son Ben and friend Ben Drew-Smythe spearheaded the banner campaign, said: "It's dangerous, everyone just uses the road as a rat run and all the lorries have no right to come down here."
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