Sinsign is a term used by Charles Peirce in his theory of signs (or semeiotic) to designate a kind of sign. Two other kinds of signs he identified are: Qualisign and Legisign). For a good introduction to Peirce's semeiotic see Part 2, "Meaning is a Triadic Relation", of John K. Sheriff's book: The Fate of Meaning: Charles Peirce, Structuralism, and Literature (Princeton, N.J.: Princeton University Press, 1989.) Here's a quote from Sheriff: "A Sinsign is a sign that is a fact. Or, in Peirce's words, it 'is an actual existent thing or event which is a sign'*"(p. 70).

*The Collected Papers of Charles Sanders Peirce, vols. 1-6, ed. Charles Hartshorne and Paul Weiss, 1931-1935; vols. 7-8, ed. A. W. Burks, 1958 (Cambridge: Harvard University Press) vol. 2, para. 245.