Lustrous, the mark is impressed.
I took 3 pictures, out on my covered porch, in natural light.
By angling the camera, the reflected light caused a shadow to appear of what looks like the base of the ?mark? ?.. which the mark itself appears to be ?a tapered/flared vase with a round base?.
See 1st photo, mark is in center, with base of mark extending into the light area and top of mark (darker shadow) pointing to upper left corner. The light area of the photo is the ?blue sky? reflection from underneath the porch roof behind me.
In 2nd photo, mark is in center, but one can barely make it out.
Hope you can make out what I attempted to define.
Thanks much, Sam