Hi John! Thanks for your opinion. Very interesting theory. But in this case "O" can mean Orion - it was the only aux.cruiser which name started from letter O. Maybe...... I am quite sure in two things:1) "O" is a letter O but not a digit 0. 2) It means something. By the way the way, in which O365 was engraveg routher interesting- it looks not like" rough, hand-made, on board the ship, with nail or needle", but more like it was done in some workshop. Best regards.