TAGIN (Aram. תָּגִין; sing., tag), special designs resembling crowns placed by a scribe on the upper left-hand corner of seven of the 22 letters of the Hebrew alphabet in a Torah, tefillin, or mezuzah scroll. A tag is generally composed of three flourishes or strokes, each of which resembles a small "zayin" – thick on top with a thin line extending downward to the letter. The center stroke is slightly higher than the two end ones. The letters which receive the tagin are שעטנזגצ (Men. 29b), including the final ן and ץ (Rashi ad loc.). According to Maimonides the omission of tagin does not invalidate the scroll since its inclusion is considered as an "exceptionally beautiful fulfillment of the mitzvah" (Yad, Sefer Torah 7:9). Ashkenazi custom, however, holds that the scrolls are invalid without the appropriate tagin (Magen Avraham and Ba'er Heitev to Sh. Ar., oḤ 36:3).
Kabbalah places great stress on the mystical meanings of the tagin. Together with the letters and words of the Torah, every additional stroke or sign is a symbol revealing extraordinary secrets of the universe and creation. The importance of the tagin is already emphasized by the Talmud in its vivid description of Moses ascending on high to find God engaged in affixing tagin to the letters of the Torah (Men. 29b).
Simḥah b. Samuel, a disciple of Rashi, copied a Sefer Tagin into his Maḥzor Vitry (ed. by S. Hurwitz (19232), 674–83). According to tradition, this Sefer Tagin authored by Joshua recorded the proper usage of the tagin as they appeared on the 12 stones which he first set up in the Jordan River and later transferred to Gilgal (Josh. 4:9, 20). On these stones were inscribed the books of Moses with the required tagin (Naḥmanides to Deut. 27:8). An annotated edition of the Sefer Tagin was issued by S. Sachs in 1866.
The tagin are the "tittles" mentioned in the New Testament (Matt. 5:18; Luke 16:17, translated as "stroke" in the New English Bible).
Eisenstein, Dinim, 300f., 433.