In the State of Washington, the State Patrol always puts the message "DUI Patrols tonight" on the readerboards in the locale where they are planning an emphasis. On their website, the usually will issue a media release for more lengthy operations.
The best things about it are: (1) drunks are notoriously poor readers, and it doesn't appear to slow business down one bit and, (2) it sure shuts up the defense attorneys, when they start mouthing off about "entrapment."
It's particularly good PR, when you can enforce the law and look scrupulously fair at the same time.