"Gott mit uns"
It means "God is with us".Why it is not "Gott ist mit uns"?
"Gott mit uns" ("God with us") is not a complete sentence, it's a phrase. It was used in this form on the coat of arms of the king of Prussia and later in the German military.
As for why they chose not to use a complete sentence like "Gott ist mit uns" (God is with us) or "Gott sei mit uns" (God be with us) - I suppose it has something to do with the fact that the phrase goes back to a Latin battle cry, which also didn't contain the verb "to be": "nobiscum deus". This battle cry is apparently an allusion to a passage in the Bible, where again the verb "to be" is omitted. Matthew 1,23: "Behold, a virgin shall be with child, and shall bring forth a son, and they shall call his name Emmanuel, which being interpreted is, God with us."
I guess the reason for the omission of "to be" in the Bible is that the passage in question translates the meaning of the Hebrew name Emmanuel. AFAIK, like Arabic, Hebrew doesn't use the verb "to be" in the present tense.
May I ask where you came across this phrase? It's a historical expression and not much used anymore today.
@Dorfl: Thanks for the confirmation! I really should learn Hebrew, it's a very beautiful language. :) I was actually on the point of buying a Hebrew language course for self-study some weeks ago, but then I thought that maybe that would be a bit too much at the moment.
I have to admit that my hypothesis that the phrase above does not contain the verb "to be" because it goes back to a translation of the name Emmanuel is a bit speculative, but apparently also the Greek original of the New Testament passage omits the verb "to be", so it could well be true.
@Siebolt: I learnt some Farsi a couple of years ago, but unfortunately by now I've forgotten most of it. Again, I can highly recommend studying it: the language has a very pleasant, melodious sound (a bit like French, actually), and, most importantly, the grammar is very accessible to the learner. No endless messing around with articles, cases and exceptions like in German. My Farsi teacher used to say that the whole grammar would fit on a postcard! Maybe that was slightly exaggerated, but the grammar really is a lot easier than in German.