Immigration Forum / USA Marriage Base / August 2008

If you have a green card or a work authorization card or if you have
some recent receipt from a USCIS application, the alien registration
number (or A #) will be printed on it, if you have one.

If you have a student (but not on OPT) or H or L similar visa, you may
not have an A #. The A # is a kind of personal file number for you.

good luck. I am sorry, I am not a lawyer so don't know all of the ways
to have one assigned to you.

another bob