Ah, you didn't know Giger did a Tarot? Well, I didn't till I found it here. And it is also found here.
There's a wealth of mystical symbols found in the multitude of Tarot decks that can be found on these two pages... including, you guessed it, the UFO Tarot.
Update (May 14, 2014): H.R. Giger passed away Monday (May 12) at the age of 74. Two online articles I recommend: the Daily Grail's Vale H.R. Giger, 1940 - 2014, and Farewell, H.R. Giger from Histories of Things to Come.
Also, I note the first Giger Tarot link has been broken, so here's a better one. I'm also including this Giger Museum link on the sidebar.