TheShah
You'll have to add some sort of additional information to each record to identify the source. Perhaps a required field that users complete one way or the other.
But there's a more interesting question not addressed here.
How is it possible that a user inserts a record into a table without doing so through a form? Are your users actually opening tables directly in datasheet view to add new records? If not, what does the difference entail?
And, as Arnel suggested, in practical terms, "Insert" and "Append" are the same thing, so perhaps that's part of the clarification needed to get a good suggestion for you.