The usual method of drawing a hexagram is with two interlaced triangles. It represents the union of opposites. The Uni Hex goes a step further. Not only are the polar opposites united, they are inseparable from each other.
It's also a visual glyph of the Thelemic pantheon in
The Book of the Law. The principle of infinite expansion, Nuit, joined with the principle of infinite contraction, Hadit, creates the microcosmic child, Heru Ra Ha, who is symbolised by the rose at the centre.
The rose can point up or down to reflect the dual, active/passive nature of Heru Ra Ha. Another way of symbolising this dual nature is to join an upright and an inverted pentagram together. It creates a traditional hexagram with a unicursal hexagram within.
A bit of trivia....
In Crowley's own copy of
The Book of Thoth he wrote an expletive and a note of complaint next to the Uni Hex on page 11. The printers had printed it upside down.
Now look at your Uni Hex card.