What is the mark placed over some German vowels?

The mark placed over some German vowels is called an Umlaut. It is two dots (¨) placed above the vowel.

Here are some examples of Umlauts:

* ä (pronounced like the "a" in "cat")

* ö (pronounced like the "oe" in "shoe")

* ü (pronounced like the "u" in "flute")

The Umlaut changes the sound of the vowel, and it's important to use it correctly when writing German. It's a unique feature of the German language that distinguishes it from other languages.