[andrewem]

The New Yorker’s eccentric diacritic is the diaeresis rather than the umlaut.

https://www.merriam-webster.com/grammar/mary-norris-diaeresi...

[adastra22]

For those wondering, they are written differently in handwriting, but are typically displayed the same in fonts.

[cryptonector]

The interwebs tells me that

| Whereas the umlaut represents a sound shift, the diaeresis indicates a specific vowel letter that is not pronounced as part of a digraph or diphthong.

I.e., graphically there's no difference. Thus I don't really care to call it one word or the other. Sure, 'diaeresis' is more correct that 'umlaut', but most English speakers -I suspect!- are more likely to recognize the latter than the former.