As mentioned in the Protected Audience explainer:

In online ad auctions for ad space, it’s sometimes useful to prevent showing an ad to certain audiences, a concept known as negative targeting. For example, you might not want to show a new customer advertisement to existing customers. New customer acquisition campaigns most often have this as a critical requirement.

This concept of “negative targeting” has been added to Protected Audience for bids coming from the contextual call, using “negative Interest Groups”. We propose extending it to bids based on Interest Groups.

The idea would be to have the possibility to link Negative Interest Groups to ads in « Positive Interest Groups ». An ad would then be:

{renderUrl : "url", metadata : object, negativeInterestGroups : [list of negative IG names]}

When generateBid() gets called, the interestGroup.ads object gets filtered according to the negative interest groups present on the browser for the same owner using the negativeInterestGroups attribute of ads.

This mechanism would:

• make it possible to combine the power of Protected Audience while respecting the fundamental constraint of marketers to acquire new customers.
• save the signature validation for the current additionalBid