Should one use quotation marks around single letters in text?

It's a matter of style. UK English tends to use single quotes whereas US tends to use double quotes. There's no additional rule for individual characters.

I don't think it's essential to use quotation marks when indicating an individual letter, but it may help for clarity. It helps when distinguishing between single-letter words and single letters, for example.

In MLA Format, the only letters that require a distinction to be made are "I" and "A," since they are words as well as letters. To my knowledge, listing the alphabet generally would look like this: "A," B, C, D, etc. I have also heard of italics and single quotes, as long as the distinction is evident. In general, words as words require quotes as well; letters, on the other hand, do not. The idea is that a capital D will never occur unless it is used as a letter, since it is not a word itself.

The Chicago Manual of Style states individual and combinations of letters within text should be italicized. However, letters indicating scholastic achievement are to be in roman type and usually capitalized (rule 6.82, 14th edition). freelance editor, B. Keith Williams