It's possible that Facebook isn't intentionally targeting Signal. When buying App Store ads, the default is to use a "broad match" for the keywords you enter -

It's possible that Facebook isn't intentionally targeting Signal. When buying App Store ads, the default is to use a "broad match" for the keywords you enter -- i.e. Apple automatically decides what keywords are similar to the keywords you selected and runs your ads against those as well. It's pretty annoying because there's no way to switch the default -- you have to remember to put your keywords in brackets to disable it -- but probably great for Apple's revenue.