Good question, I looked into this more. It turns out I had turned off the privacy informative menu a long time ago in Safari and had forgotten about it. Meanwhile the Adguard extension I use in Safari also looks like a shield (a different shield). So I thought the shield menu would have adblocking controls. So most Safari users will probably understand better than I did.
Still, I associate a "gear" with "application-wide" settings, not "per-document" or "per website" contextual settings. Maybe an ellipsis.circle would be more appropriate to indicate a menu?