Written Instruction with PIN Verified Callback. The Authorized Person(s) may elect to send an FT Instruction that bears the signature of an Authorized Instructor (a) in an original writing to an address designated by BBH from time-to-time for such purposes, (b) by fax to a fax number designated by BBH from time-to-time for such purposes, or (c) in PDF format by email to an email address designated by BBH from time-to-time for such purposes. The authenticity of that FT Instruction shall be deemed conclusive if verified by BBH as follows: