Missing lock icon in System Preferences->Sharing on El Capitan See attached image below. I have a few macs and on one of them, I cannot for the life of me figure out how to lock the Sharing tab under System Preferences. The lock is present and working on other panes that support locking. I also went to Security &amp; Privacy advanced and could not find anything there. How do I re-enable the ability to lock this pane and does anyone know why or how it got that way? My other Macs don't have this problem.

Edit: I am including another screenshot from my other Mac to show that there is indeed a lock on that pane.

I am running OS X El Capitan 10.11.2 on a Macbook Pro Retina (late 2013)
There is no lock on this screen.  There is only a lock if the setting requires an Administrator (someone with the role of Administrator) to make the changes (i.e. Security).  If anyone can make the changes then there's no need for a lock.

Make sure you're logged-in with the role of Administrator to see the preferences that you can lock/unlock.

EDIT: based on OP's new comments:
  - Log in as a user with Administrator rights.
  - Open System Preferences and select Security &amp; Privacy.
  - Click the lock icon and authenticate.
  - Click the Advanced button at the bottom and enable the Require an Administrator... in the popup window.
  - OK the change and then lock the S&amp;P preference pane.

Now when you open the Sharing preference pane you will have your lock back.