In the logo with the outlined GT Walsheim, the bar of the A has been shifted down to the next line, where it stands in for the two dots of the umlaut in “Köhli”. Such a macron-like diaeresis is particularly popular in Switzerland – cf. “Swiss umlauts” on Flickr.
The (regular) umlaut in the last image of this post is interesting, too. It is a textbook example why it sometimes would be nice to have fonts with more compact diacritics: In many languages, lines with caps (and especially lines in all-caps) can’t be set solid because umlauts and accents get in the way. I have discussed both of these topics – fancy decorative umlauts and useful compact umlauts – in my article for the freshly published fourth issue of TypoJournal (in German).