Posted:
Now, I got what you wanted to convey but it is not called vertical symmetry.
In Geometry, vertical symmetry is used when a figure can be divided in two equal parts if cut by a vertical line.Maybe you wanted to say 'rotational symmetry' as if we rotate those nos by 180 degree. Still 'symmetry' is not perfect word for it because 6 becomes 9 if rotated 180 deg.
I think,it can be perfectly described by ' rotational ambigram' term.
Yes, rotational ambigram is right. 7 is the only digit from the displayed set of digits that doesn't generate the shape of a valid number when rotated through 180 degrees. They cleverly left out 2,3,4,5!
