I've been reading about details of Torah sofrut, and after learning about the paragraph markers peh / פ (petucha) and samekh / ס (setuma), I noticed some similarly placed shin markers (mostly at the end of a sefer), but cannot find an answer in Google searches. What does it stand for? (Example: parsha VaYechi). I'm using an electronic version from Mechon Mamre similar to Keter Yerushalayim / Aleppo Codex.
The following information is recorded on the Mechon Mamre website:
That should answer your question, although I don't know where that tradition stems from. Obviously it's not the Aleppo Codex, since the Aleppo Codex is lacking most of the Torah (and I don't think these details were recorded prior to their being destroyed). I checked Rabbi Prof. Mordechai Breuer's Tanakh and I also checked the BHS, and neither of them recorded this. I have fascimiles of the Aleppo Codex and the Leningrad Codex, and neither record these symbols between other books in Tanakh (nor does the latter record it between Genesis and Exodus).
Finally, I looked at Yeivin's Tiberian Masorah and Tov's Textual Criticism of the Hebrew Bible, and they don't appear to mention it either. Regrettably, Mechon Mamre does not declare exactly which mss they are employing, save to note that they are close to the Aleppo Codex.