Title: Tau cross
Content:  The tau cross is a T-shaped cross, sometimes with all three ends of the cross expanded. It is called a “tau cross” because it is shaped like the Greek letter tau, which in its upper-case form has the same appearance as Latin letter T. Another name for the same object is Saint Anthony's cross or Saint Anthony cross, a name given to it because of its association with Saint Anthony of Egypt. It is also called a crux commissa, one of the four basic types of iconographic representations of the cross.
Title: Cross
Content:  vein included G. de Mortillet (1866), L. Müller (1865), W. W. Blake (1888), Ansault (1891), etc.  In the European Bronze Age the cross symbol appeared to carry a religious meaning, perhaps as a symbol of consecration, especially pertaining to burial. The cross sign occurs trivially in tally marks, and develops into a number symbol independently in the Roman numerals (X "ten"), the Chinese rod numerals (十 "ten") and the Brahmi numerals ("four", whence the numeral 4). In the Phoenician alphabet and derived scripts, the cross symbol represented the phoneme /t/, i.e. the letter taw, which is the historical predecessor of Latin T. The letter name taw means "mark", presumably continuing the Egyptian hieroglyph "two crossed sticks" (Gardiner Z9). According to W. E. Vine's Expository Dictionary of New Testament Words, worshippers of Tammuz in Chaldea and thereabouts used the cross as symbol of that god.
Title: Cross
Content:  The shape of the cross (crux, stauros "stake, gibbet"), as represented by the letter T, came to be used as a "seal" or symbol of Early Christianity by the 2nd century. Clement of Alexandria in the early 3rd century calls it τὸ κυριακὸν σημεῖον ("the Lord's sign") he repeats the idea, current as early as the Epistle of Barnabas, that the number 318 (in Greek numerals, ΤΙΗ) in Genesis 14:14 was a foreshadowing (a "type") of the cross (the letter Tau) and of Jesus (the letters Iota Eta). Clement's contemporary Tertullian rejects the accusation that Christians are crucis religiosi (i.e. "adorers of the gibbet"), and returns the accusation by likening the worship of pagan idols to the worship of poles or stakes. In his book De Corona, written 
Title: Cross
Content:  characters, consisting of an arrangement of boxes or the fourfold arrangement of other characters, including the archaic cuneiform characters LAK-210, LAK-276, LAK-278, LAK-617 and the classical sign EZEN (𒂡). Phoenician tāw is still cross-shaped in Paleo-Hebrew alphabet and in some Old Italic scripts (Raetic and Lepontic), and its descendant T becomes again cross-shaped in the Latin minuscule t. The plus sign (+) is derived from Latin t via a simplification of a ligature for et "and" (introduced by Johannes Widmann in the late 15th century). The letter Aleph is cross-shaped in Aramaic and paleo-Hebrew. Egyptian hieroglyphs with cross-shapes include Gardiner Z9 &ndash; Z11 ("crossed sticks", "crossed planks"). Other, unrelated cross-shaped letters include Brahmi ka (predecessor of the Devanagari 
Title: Crossed letter
Content:   A crossed letter is a manuscript letter which contains two separate sets of writing, one written over the other at right-angles. This was done during the early days of the postal system in the 19th century to save on expensive postage charges, as well as to save paper. This technique is also called cross-hatching or cross-writing. A cross letter is distinct from a palimpsest, as cross-hatched manuscripts were written this way at one sitting or for the same purpose (such as a diary), rather than being re-used later.
Title: Christian symbolism
Content:   The shape of the cross, as represented by the letter T, came to be used as a "seal" or symbol of Early Christianity by the 2nd century. At the end of the 2nd century, it is mentioned in the Octavius of Minucius Felix, rejecting the claim by detractors that Christians worship the cross. The cross (crucifix, Greek stauros) in this period was represented by the letter T. Clement of Alexandria in the early 3rd century calls it τὸ κυριακὸν σημεῖον ("the Lord's sign") he repeats the idea, current as early as the Epistle of Barnabas, that the number 318 (in Greek numerals, ΤΙΗ) in  
Title: Instrument of Jesus' crucifixion
Content:  the sign of a cross; and when a man adores God with a pure mind, with hands outstretched. Thus the sign of the cross either is sustained by a natural reason, or your own religion is formed with respect to it." In language very similar to that of Minucius Felix, Tertullian, too, who distinguished between stipes (stake) and crux (cross), noted that it was the cross that people associated with Christianity. And he indicated that the shape of the cross is that of the letter T: "The Greek letter Tau and our own letter T is the very form of the cross, which (God) predicted would 
Title: Descriptions in antiquity of the execution cross
Content:  set the mark Tau upon the foreheads of the men.' Now the Greek letter Tau and our own letter T is the very form of the cross, which He predicted would be the sign on our foreheads." (''omnes fideles [...] signatos illa nota scilicet de qua Ezechiel: Dicit dominus ad me, Pertransi in medio portae in media Hierusalem, et da signum Tau in frontibus virorum. Ipsa est enim littera Graecorum Tau, nostra autem T, species crucis, quam portendebat futuram in frontibus nostris''). The universality of the Early Christian practice of tracing the sign of the cross on the forehead, not limited to the Roman 
Title: Descriptions in antiquity of the execution cross
Content:  "wherever the fathers came across the number 300 in the Old Testament they took it to be a mystical prefiguring of the cross of Christ". Tertullian (c. 155 – c. 240), writing in Latin, remarks that the Greek letter τ and the Latin letter T have the same shape as the execution cross: "Ipsa est enim littera Graecorum Tau, nostra autem T, species crucis". Non-Christians too of the time when in the Roman Empire criminals were executed by crucifixion, considered identical the shape of the execution cross (σταυρός in Greek) and that of the letter tau. In the Trial of the Court of the 
Title: Christian cross
Content:   The Christian cross, seen as a representation of the crucifixion of Jesus on a large wooden cross, is a renowned symbol of Christianity. It is related to the crucifix (a cross that includes a corpus, usually a three-dimensional representation of Jesus' body) and to the more general family of cross symbols, the term cross itself being detached from the original specifically Christian meaning in modern English (as in many other western languages). The basic forms of the cross are the Latin cross with unequal arms and the Greek cross with equal arms, besides numerous variants, partly with confessional significance, such as the tau cross, the double-barred cross, triple-barred cross, cross-and-crosslets, and many heraldic variants, such as the cross potent, cross pattée, cross moline, cross fleury, etc. For a few centuries, the emblem of Christ was a headless T-shaped Tau cross rather than a Latin cross. Elworthy considered this to originate from Pagan Druids who made Tau crosses of oak trees stripped of their branches, with two large limbs fastened at the top to represent a man's arm; this was Thau, or god.

Question: what is the cross on a letter t called?
Answer: arm.
crossbar.