Question

Bava Metzia 25a: “What does he announce? The number. Why specifically three? Even two as well? Ravina said: And he announces it.”
Rashi: “He announces ‘coin’—I found coins. Therefore, come and give a sign, for the minimum of ‘coins’ is two.”
Seemingly, once we say that for finding two coins one does not announce the number because the minimum plural is two, then from that point on, in every announcement of a lost item the minimum plural should be three coins, and then three is no longer a distinguishing sign either.
Of course, one could continue this to four coins, then five, and so on ad infinitum.
So the question is: what is the stopping criterion?