“Semiotic provides a basis for understanding the main forms of human activity and their interrelationship, since all these activities and relations are reflected in the signs which mediate the activities … In giving such understanding, semiotic promises to fulfil one of the tasks which traditionally has been called philosophical. Philosophy has often sinned in confusing in its own language the various functions which signs perform. But it is an old tradition that philosophy should aim to give insight into the characteristic forms of human activity and to strive for the most general and the most systematic knowledge possible. This tradition appears in a modern form in the identification of philosophy with the theory of signs and the unification of science, that is, with the more general and systematic aspects of pure and descriptive semiotic.”

Die Möglichkeit aller Philosophie ... dass sich die Intelligenz durch Selbstberührung eine Selbstgesezmäßige Bewegung - d.i. eine eigne Form der Tätigkeit gibt.
Schriften, p. 63, as translated in Walter Benjamin: Selected Writings: Volume 1, 1913-1926 (1996), p. 133

Source: Signs, Language and Behavior, 1946, p. 238; as cited in: Adam Schaff (1962). Introduction to semantics, p. 88-89

100 Years of Mathematics: a Personal Viewpoint (1981)

Source: Signs, Language and Behavior, 1946, p. 19

Variant translation: Philosophy is not a theory but an activity. A philosophical work consists essentially of elucidations. The result of philosophy is not a number of "philosophical propositions." but to make propositions clear.
Original German: Der Zweck der Philosophie ist die logische Klärung der Gedanken. Die Philosophie ist keine Lehre, sondern eine Tätigkeit. Ein philosophisches Werk besteht wesentlich aus Erläuterungen. Das Resultat der Philosophie sind nicht „philosophische Sätze“, sondern das Klarwerden von Sätzen. Die Philosophie soll die Gedanken, die sonst, gleichsam, trübe und verschwommen sind, klar machen und scharf abgrenzen.
1920s, Tractatus Logico-Philosophicus (1922)
Context: Philosophy aims at the logical clarification of thoughts. Philosophy is not a body of doctrine but an activity. A philosophical work consists essentially of elucidations. Philosophy does not result in 'philosophical propositions', but rather in the clarification of propositions. Without philosophy thoughts are, as it were, cloudy and indistinct: its task is to make them clear and to give them sharp boundaries. (4.112)

Source: "Foundations of the Theory of Signs," 1938, p. 43

Excellence: Can We Be Equal and Excellent Too? (1961).

[O] : Introduction, 0.6
Semiotics and the Philosophy of Language (1984)
Context: When semiotics posits such concepts as 'sign', it does not act like a science; it acts like philosophy when it posits such abstractions as subject, good and evil, truth or revolution. Now, a philosophy is not a science, because its assertions cannot be empirically tested … Philosophical entities exist only insofar as they have been philosophically posited. Outside their philosophical framework, the empirical data that a philosophy organizes lose every possible unity and cohesion.
To walk, to make love, to sleep, to refrain from doing something, to give food to someone else, to eat roast beef on Friday — each is either a physical event or the absence of a physical event, or a relation between two or more physical events. However, each becomes an instance of good, bad, or neutral behavior within a given philosophical framework. Outside such a framework, to eat roast beef is radically different from making love, and making love is always the same sort of activity independent of the legal status of the partners. From a given philosophical point of view, both to eat roast beef on Friday and to make love to x can become instances of 'sin', whereas both to give food to someone and to make love to у can become instances of virtuous action.
Good or bad are theoretical stipulations according to which, by a philosophical decision, many scattered instances of the most different facts or acts become the same thing. It is interesting to remark that also the notions of 'object', 'phenomenon', or 'natural kind', as used by the natural sciences, share the same philosophical nature. This is certainly not the case of specific semiotics or of a human science such as cultural anthropology.

Further Studies in a Dying Culture (1949), Chapter IV: Consciousness: A Study in Bourgeois Psychology