Why Pencil Icon is shown to registered user

It generally means that one of those roles has been granted permissions that warrant access to the admin area, such as moderation or reviewing abuse.  Review all the permissions.

we have unchecked all permission to registered user role but no effect

Don't do that, that is going to make your situation worse.  You also need to check the Everyone role.   Only remove elevated permissions like those pertaining to review abuse or moderation.  You will also need to make sure these types of permissions are not granted at the group of role level (or verify these users aren't group owners/managers somewhere.