6.124 Logical propositions describe the frame of the world, or rather they present it. They “deal” with nothing. They presuppose that names have meaning and elementary propositions sense: And this is their connection with the world. It is clear that it must show [anzeigen] something about the world that certain combinations of symbols – which essentially have a specific character – are tautologies. Herein lies the decisive thing. We said that much in the symbols that we use is arbitrary, much not. In logic only this latter expresses anything: That means however that in logic we do not express what we want with the aid of signs, but rather in logic the nature of the constitutionally necessary signs exhausts itself: If we are acquainted with the logical syntax of some sign language, then all the propositions of logic are already given.
I originally had “physically necessary” for naturnotwendigen because that is the only meaning given by my dictionary for this word, but I think "constitutionally necessary" might be a better translation.
The rest I think makes sense and sounds right, apart from the slightly worrying (because it still is not wholly clear what these are) talk of names and elementary propositions, but I assume these now mean basically just “words” and “propositions” or “sentences” (like p and ~p) that are combined in logic in various ways. The really worrying thing is the claim that the existence of tautologies must show something about the world. What does it, could it, show except itself? Well, Wittgenstein does not claim that it shows anything more than this.
Black (p. 331) points out that the image of scaffolding (Gerüst) occurs also at 3.42 and 4.023.