I'm sorry we have an pornographic ad show up and ruin the experience here at Safebooru.
I've seen the ad too. I've alerted our admin to the ad problem and I hope that we can do something about it soon.
In a parallel, here is a link to an ongoing fundraiser for Safebooru and other 'boorus. The funds go to help purchase better hardware and upgrade softwares and might help stave off bad ads:
I don't know if the link is allowed due to it being an indirect fundraiser, but I will post the link to a stickynote , if it is acceptable by admin.
Adendum: No one should have to use an ad-blocker program when browsing here at Safebooru, but if an ad-blocker has to be used because of foul ads, I would suggest looking at 'ABP' or 'Ad Block Plus'. By default, ABP has everything blacklisted, so you add those 'safe' sites to a whitelist.