The propositional sign consists in the fact that its elements, the words, are combined in it in a definite way.
The propositional sign is a fact.
3.141 The proposition is not a mixture of words. - (Just as the musical theme is not a mixture of tones.)
The proposition is articulate.
3.142 Only facts can express a sense, a class of names cannot.
3.143 (2) That the propositional sign is a fact is concealed by the ordinary form of expression, written or printed.
For in the printed proposition, for example, the sign of a proposition does not appear essentially different from a word.
(Thus it was possible for Frege to call the proposition a compounded name.)
3.144 States of affairs can be described but not named.
(Names resemble points; propositions resemble arrows, they have senses.)