Most of the attention focused on Facebook this week has centered on the company’s oversight board and its decision to permit the platform’s ban of Donald Trump. Meanwhile, a weirder controversy about Facebook’s ads and privacy policies has been playing out between the social media giant and encrypted messaging service Signal. Signal initiated the spat on May 4 when Jun Harada, the company’s head of growth and communication, posted on the Signal blog about a set of ads that Harada said Signal had tried to run on Instagram. Instead, Facebook blocked the ads and shut down Signal’s adve...