To sign the @ symbol you us an "A" handshape and circle it in the air as
if drawing the symbol:
@
It really isn't an issue if you do the movement clockwise or
counterclockwise.
I've yet to see a consensus on that.
Warning! This next version is rarely used in ASL.
It is NOT used in phrases like "at least."
Instead of signing "AT" in "at least you can" you would
sign something like, "YOU STILL CAN ..."
Instead of signing "at last" you would sign "pah"
(finally).
Instead of signing "We will meet at my home tomorrow," you would
sign, TOMORROW MEET MY HOME.
Instead of signing "Where at?" You would just sign
"WHERE?" and use an appropriate question facial expression.
I'm showing this sign here not so you will use it, but rather so you can recognize it if you see
it.
AT: