There are many reports at the Google AdSense Help forum with publishers complaining that Google is displaying weird characters on their ads. Here is a picture of one:
Here is another picture, this one is from my personal blog:
Notice the ad at the top right showing weird characters.
Google has confirmed the bug in those threads and said:
We're aware of the issue and we're looking into it.
Currently, there is no ETA for when the issue will be resolved but it is good to know Google is aware of the issue and actively working on fixing it.