I regret it hasn't been quite clear that when I said to Grendl «With "ñ" we have a new sign different from de original one indicating that another "n" was not written there but might be read» I was referring to the medieval Latin abbreviations system. That was the context. On the other hand, I must insist one more time that «the Spanish tilde virgulilla it's not a palatalization mark of the system because it doesn't belong to the system as a tool for marking palatalization»
In your new message you are not talking about palatalization marks but about graphical distinctions. But I imagine you realize that, as I've said, one thing is to use a sign like a visual index in order to distinguish two signs (like when it's taught to little kids, for example) and another very different one is that that sign is a functional mark of the writing system. Otherwise, the rightmost stroke of "m", for example, could be considered as a mark of the written system -as so adequately pointed out our colleague Anton Sherwood-, which we all know it is not true.
By the way, just a minor correction, the "n" is not in Spanish a dental phoneme but an alveolar one.