We know Hermione didn’t send herself a signal she could notice instantly on a second iteration. As of ch76, we do
not know if she sent herself a signal not instantly noticable.
You might not want to use a signal that could be detected by yourself during an obliviation event in order to make sure the signal isn’t telegraphed to the obliviator.
Harry might think that if one needed to signal obliviation, it might be best to detect it safely in the future, unless he thought he could make use of an instantly detectable signal and a tactical response would be worth risking interception. In Ch. 6 he risked interception of the signal (he told the potential obliviator McGonnagal about it) in order to forestall obliviation. I doubt that that tactic would work with Mr. Hat and Cloak/Ms. Veil/...
We know Hermione didn’t send herself a signal she could notice instantly on a second iteration. As of ch76, we do not know if she sent herself a signal not instantly noticable.
You might not want to use a signal that could be detected by yourself during an obliviation event in order to make sure the signal isn’t telegraphed to the obliviator.
Harry might think that if one needed to signal obliviation, it might be best to detect it safely in the future, unless he thought he could make use of an instantly detectable signal and a tactical response would be worth risking interception. In Ch. 6 he risked interception of the signal (he told the potential obliviator McGonnagal about it) in order to forestall obliviation. I doubt that that tactic would work with Mr. Hat and Cloak/Ms. Veil/...