ok sorry guys. the context is a letter sent to a customer from a bank in which they are stating the details of the bank account she has opened.
so there is a heading that says "account type/designator". under this heading there is the name of the account "Bonus Saver". the account has been opened with $100. so i suppose that i can translate designator as "beneficiario". i agree with mylam. i think here they are referring to the phrase Bonus Saver, the name of the account on which the $100 have been deposited. so, chaucer, do u think i could still translate it as beneficiarioi? sorry i did not ask properly before in my haste.