No, you don't need a sign off for any CFI knowledge (written) tests. That includes FOI, CFI, and CFII. I think AGI is included as well. If you don't pass you will need an endorsement.
You have to read the FAR's very carefully on this one.
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According to FAR 61.183 (d) Recieve a logbook endorsment from an authorized instructor on the fundamentals of instructed listed in 61.185 of this part appropriate to the required knowledge test.
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But then there's (e) Pass a knowledge test on the areas listed in 61.185(a)(1) of this part.
Notice how the two aren't together in one part there's (d) and (e) VS (d) and (d)(1) as they would be for PPL, IA, or CPL. Under those parts (PPL, IA, CPL) you will see that your flight instructor must certify that you are prepared to take the required knowledge test.