If these bar marks are the actual “watermark” it is genius.

If it were any other shape or any other location on the card it might be detectable by causal observance - BUT because it is slightly off set and up from the existing black ink bars, yet the same shape, when you look at the black bars your eye gets a temporary imprint of the shape.

When you glance around the edge of the card the watermark gets camouflaged with the temporary visual phenomenon known as light imprinting.

It happens to everyone, when you look at an image that has contrast and for a few seconds you can look away and still see the shape lingering in your vision.

This watermark would be very difficult to detect. You can see the temporary light imprinting yourself. But zoom in and you can barely see the watermark which is camouflaged to the casual observer.

This is Brilliant if is true.

The idea needs to be implemented in the future if not done already.