World Cup fans flying England flags on their cars have been urged to consider animals and other road users.
The warning comes after police in Hampshire received reports from horse owners saying the flapping banners startle some animals.
Motorists are also warned they could face assault charges if an unsecured flag flies off and injures a cyclist or pedestrian.
Many drivers are displaying flags in the run up to the football tournament.
Pc Derek Grist, equine liaison officer, said: "It is commendable the nation is getting behind their football team but I do have concerns that motorists may cause an animal to bolt and possibly cause injury to itself, its rider or innocent passers-by.
"We are not trying to be killjoys, all we ask for is a little bit of consideration."
But Tim Murray of South Coast England Fans told the BBC News website he had never seen a flag fall off.
He added: "I can see the issue about them being securely fixed is a sensible one.
"But I think they're being a little bit petty and perhaps time could be directed towards things which are more serious, for example true criminals."