It's part of their style guide. The diaresis in this case indicates that the second vowel is part of another syllable. The New Yorker similarly uses similar spe

It's part of their style guide. The diaresis in this case indicates that the second vowel is part of another syllable. The New Yorker similarly uses similar spellings such as naïve. It's actually not a font or typeface: it's spelling consistent with their style guide.