Amsterdam Coffeeshop Directory Forums

After spending the last 3 weeks all over the Netherlands , often by car ,along the main highways at times I have a question ...We constantly saw these big USA style billboards (Please NL -don't go there) I mean every 5 KMs ,and they say- Eerst een Bob ,dan een fluitje,Daar Kan je mee thuis Komen ....
Now we know what they SAY , but what the hell does it MEAN ? Thanks for any answer ...

It's to remind people not to drink and drive. Bob is the fictional name of the person that's driving you home after you've had a beer.