Depending on the font, they are N, S and Z.
Mississippi
ALL letters have at least one line of rotational symmetry. However - if you mean reflective symmetry, the letters F, G, J, L, P, Q, R, S, & Z do not.
H,i,o,x
4
There are 10 letters in the alphabet that achieve rotational symmetry when displayed in their capital form. These letters: A, H, I, M, O, U, V, W, X, and Y.
H, I, O, X. In some fonts the symmetry may not apply.
E s i o
H, I, O, and X have rotational symmetry.
The answer depends of the font.In broad terms, in the upper case letters:F, G, J, L, P, Q and R.The others have reflective (or line) symmetry, or they have rotational symmetry, or both.
H, I, N, O, S, X, and Z
A nonrectangular parallelogram has rotational symmetry, but not line symmetry. Additionally, shapes such as the letters S, N, and Z can be rotated to show rotational symmetry, although they do not have line symmetry.