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:

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.