Section 5--104. Formal requirements. A  letter  of  credit,  confirmation,  advice, transfer, amendment, or  cancellation may be  issued  in  any  form  that  is  a  record  and  is  authenticated: (a) by a signature, or (b) in  accordance  with  the agreement of the parties or the standard  practice referred to in subsection (e) of section 5--108.