How can an author mark the update date of a node to be visible or hidden for visitors? I want to let the author to specify whether node update date should be visible to visitors or not, per node (not node types) with a checkbox at node insert/edit form?

Update: 
I know how to use fields but I considered using something other than a new field. Something like variables.

Because I just want to save a simple Boolean value and I think fields will push an unreasonable overhead to Drupal for such a simple task.
You could add new field as a checkbox author check if he needs the update date visible to visitors.

Use panels and page manager to build a custom page view for that node type

Add visibility rule to display the update date if the checkbox field is checked