Sabine, as far as I know uggs have three markings:
-a tag on the inside with the type of leather/shearing, location made, and some sort of serial number
-an imprint on the bottom, different from style to style
-a mark on the back of the heel that's visible that sats ugg australia.
the walking store, norstroms, and a few others are carrying uggs if you want to see them irl first. the marks may be different from style to style... what uggs are you looking at?