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Explanation: I'm fairly sure "endosables a simple firma" is saying that the CD can be transferred to someone by "endorsement" which already implies a signature. The CD is then payable to the bearer. For example when you endorse a check you sign it and it becomes payable to the bearer, who cashes it.
I think "transferrable with endorsement" covers it, but if you want to be more explicit you could say something like "endorsable with signature"