So what? I can't imagine any possible way it would be unclear whether someone entered a credit card number or a negative number. They have different numbers of "-" in completely different places. Am I missing something?
> I'd argue that it would also be worthwhile to request clarity from the user when an input hits a filtering rule so that they can make clear their intent... e.g. if you assume that they're using "-" as a symbol for separation rather than simply follow that assumption, ask if that's the case and list other optional valid contexts for that symbol so they can be explicit. If they choose None of the Above or a context that is inappropriate for the field, inform them of that.
That sounds like such bad usability I'd assume you were joking if the rest of your post didn't sound so serious.