The question depends on what you consider to be English letters. The letters that this site uses are Roman letters.
Letters with both horizontal and vertical symmetry are: (lower case) - lox (upper case) - HIOX
,;'rtyuiop[][pouyfdfghjkl;'/.,mncvbnm,
No. DAY is a word typed in upper case letters. It is not a line - whether of symmetry or otherwise.
Lower case "o" and "x" both have two lines of symmetry. Upper case letters with two lines of symmetry are: "O," "X," "H" and "I."
The letters A H I O T X Y all have a vertical line of symmetry (as they look the same on the left as they do on the right).
O,I,H,andX * * * * * Not forgetting N, S and Z.
Lower case A doesn't have a line of symmetry. Upper case A has a vertical line of 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.
lower case i has 1 line of symmetry upper case I has 2 lines of symmetry
The letters: I O H X o x all exhibit bilateral symmetry and rotational symmetry, with O and X exhibiting it in both upper and lower case.
As written in lower case in this font (as waist), 2: the letters w and iIf written in upper case in this font (as WAIST), 4: the letters W, A, I and T
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.