Axis History Forums says it's difficult to translate, as literally it just means 'And Yet', or 'Nevertheless', and is meant to convey is that, despite all hardships, the Iron Division will stand the test of time. Technically it doesn't carry National Socialist ideology, and the moderators seem to be letting it slide.
I've also been seeing that people have been making their own play-on-words with the trend. Moderator Farnhamia has a menacing "Und DEAT" imposed on it's flag, and yours truly has chosen a more clerical approach.
If I had to guess how long this trend will last for, I'm placing my money on a week at best.
Anyways, if anyone has any thoughts on why this trend has reoccurred or further opinions on the phrase, go ahead and "Und Discuss"
Original Freikorps Flag:

Scomagia's take on the issue:

Farnhamia's more intimidating stance:









