Apparently that is actually the measurement of gravity in the Plato scale. The beer has 4.9% abv, and 12 degrees of gravity (??)

Here's what I found from wikipedia

"By considering the original gravity, the brewer or vintner obtains an indication as to the probable ultimate alcoholic content of their product. The OE (original extract) is often referred to as the "size" of the beer and is, in Europe, often printed on the label as Stammwürze or sometimes just as a percent. In the Czech Republic, for example, common descriptions are "10 degree beers", "12 degree beers" which refer to the gravity in Plato of the wort before the fermentation."