Departments of the same bank or subsidiary(ies)? You may be OK in simply referring them over, but I prefer an opt in that says something along the lines of "yes I am interested in learning more about investments...I understand that these ... are not, not..."
It simply helps to keep lines of communication clear and also aids in tracking referrals for any incentive programs that may exist.
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Life without Jesus is like an unsharpened pencil - it has no point.