Unfortunately I don’t have style books to hand, but practice on this has varied in English. 100 years ago, the convention was to write only the first and the last letter of the obscenity, and to put dashes between them: d—d. The contemporary practices I have seen are to put ellipses between the first and last letter (f…k), to put asterisks between the first the last letter (f**k), and to put an asterisk in place of the first vowel (f*ck). The use of Random shift key symbols is a comic strip convention, and I have not seen it in books.
Of the three conventions, replacing just the vowel is a lot clearer, but for that reason if there’s more risk of offence, and I would regard it as more informal. Online, the norm I have seen is multiple asterisks. In newspapers, the norm I have seen is ellipses.