Hallo, hinter die Zahl. 100 € Gruß

Placement of the € sign varies across countries: When you write a German text targeted at an audience from Germany, I‘d put it behind the number, together with a spacing. If the audience is from Austria, I'd put it in front of the number, also with a spacing. In English texts, I'd recommend to put it in front, but without the spacing. "Placement of the sign also varies. Partly since there are no official standards on placement, countries have generated varying conventions or sustained those of their former currencies. For example, in Ireland and the Netherlands, where previous currency signs (£ and ƒ, respectively) were placed before the figure, the euro sign is universally placed in the same position. In many other countries, including France, Germany, Italy and Spain, an amount such as €3.50 is often written as 3,50 € instead, largely in accordance with conventions for previous currencies and the way amounts are read aloud. In English, the euro sign—like the dollar sign ($) and the pound sign (£)—is placed before the figure, unspaced, as used by publications such as the Financial Times and The Economist. When written out, "euro" is placed after the value in lower case; the plural is used for two or more units, and euro cents are indicated with a period, not a comma, e.g., 1.50 euro, 14 euros." http://en.wikipedia.org/wiki/Euro_sign#Use http://en.wikipedia.org/wiki/Linguistic_issues_concerning_the_euro