Saying "this is a hand" while gesturing with one's hand is a meaningful use of language. If one knows that their hands are called "hands", then one knows that one has things called "hands". Hands are the things we call "hands". If one knows that we have things called "hands", one knows that we have hands. If one knows that we have hands, and knows that we call hands "hands", then one surely knows that "this is a hand" is true. The "is true" in the preceding sentence is superfluous here.