I'd say they were marks used when the door was cut for the lock, so that they didn't get mixed up when removed for paint etc. I'd expect to find a similar mark somewhere on the original door as well.
There were marks like those on all the components of our church pews, as obviously all the pews were constructed, then moved in pieces and re-assembled on site. I found to my cost that although they all looked the same, the parts were not interchangeable!