Agreement with the truth-possibilities can be expressed by co-ordinating with them in the scheme the mark "T" (true).
Absence of this mark means disagreement.
4.431 The expression of the agreement and disagreement with the truth-possibilities of the elementary propositions expresses the truth-conditions of the proposition.
The proposition is the expression of its truth-conditions.
(Frege has therefore quite rightly put them at the beginning, as explaining the signs of his logical symbolism. Only Frege's explanation of the truth-concept is false: if "the true" and "the false" were real objects and the arguments in ~p, etc., then the sense of ~p would by no means be determined by Frege's determination.)