Motorists driving on expressways around Flint are getting surprised by a stunning tactic that the Genesee County sheriff has been using to fight the flow of illegal drugs -- one that legal experts said will not withstand a court challenge.

At least seven times this month, including Tuesday, motorists have said they have seen a pickup towing a large sign on I-69 or U.S.-23 that depicts the sheriff's badge and warns: "Sheriff narcotics check point, 1 mile ahead -- drug dog in use."