From the introduction of the 1941 Duden edition (a German dictionary). § I.2. regulates the letter style: “Foreign words and expressions that occur in Latin [i.e. Roman] type, e.g. adagio, a conto, à condition, km, always have to be rendered in Latin type, even if the rest of the text is written or printed in German [i.e Blackletter] letters.”

In response to http://twitter.com/#!/rnkeller/status/29262221604

Guess whose birthday is today? Many returns!

Hey @googletranslate, it’s only one character, but it still makes a difference!

Today is Round Numbers Day. Oh no, now I’ve ruined it!

‘Me too!’—Shouldn’t that be ‘Me neither’?

Differences in construction: The figure 8.
Florian Hardwig: The forms of primary script (ATypI 2007)
http://florian.hardwig.com/manuscribe