Security stored on items
Access rights (security) are stored on the item itself, in the __Security
field. You can see the contents of this field in a few ways:
Security Details tab
In the Content Editor, under the Security ribbon tab, click the Details button and you will see the following tab:

Raw field values
If you want to be able to copy the security from one item to another (or manually manipulate the security settings [not recommended]), you can show standard fields (View ribbon tab -> Standard Fields) and show raw values (View ribbon tab -> Raw Values):

Access Viewer
To see the effective security permissions for an item, you can use the Access Viewer (Security ribbon tab -> Access Viewer). This shows not just what security is set on the current item, but how the ancestors' security affects this item for a given user or role:
