The emu is not decorative. Its orientation through the year is used to time the collection of emu eggs, and the connection is direct enough that a person who can find the shape can read the season off it.
In autumn the figure appears in the evening sky in a posture read as the female emu sitting, and that is when the birds are on their nests and the eggs may be taken. Later in the year the shape is oriented differently and the season is read as past. Different groups across the continent describe the postures differently, and the timing follows local conditions, but the principle holds widely.
There is a rock engraving at Elvina Track in Ku-ring-gai Chase National Park, north of Sydney, showing an emu in a posture that matches the sky figure, positioned so that the engraving and the constellation align at the relevant time of year. How deliberate the alignment is has been argued over, but the engraving and the geometry are both there and have been measured.
The general caution applies. Australia holds hundreds of distinct traditions, and while the emu is unusually widely recognised, what it means and how it is read is local and is owned. The atlas records the figure and the practice of reading it, not a single account presented as the account.