Does it matter which wrist is on top?
Generally, you should place your dominant hand (the hand you write with) on top when crossing your wrists. However, if you accidentally place your non-dominant hand on top, the sign will still be easily understood by others.
Is this the same sign used in Austrian Sign Language?
No, this is the American Sign Language (ASL) sign used to refer to the country. Deaf people in Austria use Austrian Sign Language (ÖGS), which has its own distinct vocabulary and its own native sign for their country.
What handshape is used for this sign?
You will use the 'X' handshape for both hands. To make this shape, curl your middle, ring, and pinky fingers into your palm, place your thumb over them, and hook your index finger as if you are mimicking a hook.