If you see such ad, do report it.
All ads on Project-GC is served by Google. They do not have porn ads, or should not have. Any partner they have can probably put new images in and they are most likely only reviewed by automated services. You should not see such ads on Project-GC.
The alternative is if they are coming from elsewhere (evil intent extensions to the web browser, virus, etc).
Project-GC can however do nothing about it. Reporting them is the only way. Every Google ad should have a link for that, probably in one of the corners.