I'm seeing the same exact issue (iPhone 6S, iOS 12.2): signposts are not visible in untethered mode but energy logs are
The signposts being referred to are the kernel's signposts (i.e. kdebug rather than os_signpost), and we use that internally for development. This option should never show up on a healthy external device. We're investigating what happened. Have either of you installed a provisioning profile from https://developer.apple.com/bug-reporting/profiles-and-logs/ ?