My first memory of an X graphic was 'where the treasure was buried' . . . you remember - X marks the spot.
Then via history books I loved the tree trunks carved by white explorers to say 'dig here to find his remains'.
As a found photograph & post card collector, I have always been delighted when a card comes to me with 'extra information', 'notations' or 'free hand additions'.
I've scanned the two largest photographs first, both have a biro cross over the person in question.
The large group photo shows (my wife), Barbara's father; Mr Bruce Heath in Moscow at an international bankers convention in 1962 . . . yep that's where to find him!