A Google AdWords Help thread reports from several advertisers that even though they have completed and passed the Google AdWords Professional exam, they are not able to retrieve the logo to place on their web sites.
This is not a wide spread issue, as far as I can tell. It seems like there might be a bug with certain accounts. Only some are reporting the issue as taking longer than 2 weeks. Typically, you pass the exam and two weeks later you should be able to place the logo or seal on your web site. But some seem to have been in the queue for months.
One advertiser said he finally got through to a Googler who confirmed his issue and hopes to resolve it for him in the upcoming days. He said:
So I finally made contact with a real person at Google via the Live Chat in the Help Section. She agreed that 4 weeks was too long and took my exam information and has promised to look into the problem and email me as soon as she has an answer.
I was actually amazed that the chat connected to someone in less than 30 seconds! Some of my faith has been restored...
Like I said, I am not sure how widespread the issue is, but it does seem to be an issue for some.
Forum discussion at Google AdWords Help.