Theoretically, forwardslash and I (the coders) could see comments that you upvote, since the app needs to know and that data isn't encrypted. Off the top of my head, we could probably write the app in such a way that we can't know, but I am not sure if that information could be useful in a functional/moderation sense in the future. -That is, maybe you want to see the comments that you have upvoted. Actually, if you visit my profile mk, you can see your interactions with me there. So that uses this comment upvote data, but it's not post-specific, and only you can see it.

In reality, we don't, and I don't think we should. I don't think other users should see your comment upvotes. I haven't spent a lot of time thinking on why, but I am against it.

As for clicks and page histories, no. The only thing we log in terms of non-vote/comment/share activity is the last time you as a user logged in (not visited, but actually logged in). We don't log posts or links visited, IP address, entry page, visit length, or anything like that. The app doesn't have activity logs. Our Piwik Analytics does some of that with the accuracy of the first 3 digits of your IP (the last 9 are masked, so we only know your country), but even that data is wiped every 24 hours. If you had access to our analytics data, you could probably figure out the countries some users in the last 24hrs were from based on some of the pages they visited (like the settings page).

The Hacker News source code did log aggressively, but we removed all of that.