[Claud]

I would think a silent "Amen" would be appropriate then, don't you?

Of course! But if I forget, I'll forget silently too. :)

As I'm usually kneeling, I doubt if the priest has any doubt about what I believe when I'm receiving.

[dcs.trad]

I sometimes forget, too, because I'm used to assisting at the TLM. Not that I've been to a Novus Ordo lately.