I was going to post that myself, having recently encountered that sign. But then, I remembered my promise not to talk about Canada any more...

I was also stopped at an OPP checkpoint on the Trans Canada Hwy and asked the officer what was up. Checking for drunk drivers, he said. When I asked if the checkpoint would still be there later (the line was very long) he said "no, don't worry about it - go ahead and get drunk. We'll be gone by the time you get back." His laughter made me believe he almost wasn't kidding. Nice guys, the OPP.