The "Christian" cross "was an emblem to which religious and mystical meanings were attached long before the Christian era." - Chamber's Encyclopaedia, 1969 ed.
The pagan Romans used the symbol of the cross before and during the early days of Christianity: "These crosses were used as symbols of the Babylonian sun-god ... and are first seen on a coin of Juolius Caesar, 100-44 B.C., and then on a coin struck by Caesar's heir (Augustus), 20 B.C." - The Companion Bible.
And Prof. G.F. Snyder points out that "The sign of the cross has been a symbol of great antiquity, present in nearly every known culture. .... The universal use of the sign of the cross makes more poignant the striking lack of crosses in early Christian remains, especially any specific reference to the event on Golgotha. Most scholars now agree that the cross, as an artistic reference to the passion event, cannot be found prior to the time of Constantine." - p. 27, Ante Pacem - Archaeological Evidence of Church Life Before Constantinte.
The Baptist NT scholar W.E. Vine wrote about "Cross":
"STAUROS ... denotes, primarily, an upright pale or stake. On such malefactors were nailed for execution. Both the noun and the verb stauroo, to fasten on a stake or pale, are originally to be distinguished from the ecclesiastical form of a two beamed cross. The shape of the latter had its origins in ancient Chaldea, and was used as the symbol of the god Tammuz (being in the shape of the mystic Tau, the initial of his name) in that country and in adjacent lands, including Egypt. By the middle of the 3rd cent. A.D. the churches had either departed from, or had travestied, certain doctrines of the Christian faith. In order to increase the the prestige of the apostate ecclesiastical system pagans were received into the churches apart from regeneration by faith, and were permitted largely to retain their pagan signs and symbols. Hence the Tau or T, in its most frequent form, with the cross-piece lowered, was adopted to stand for the cross of Christ." - p. 248, An Expository Dictionary of New Testament Words, Thomas Nelson, 1983 printing.
"In ancient Israel, unfaithful Jews wept over the death of the false god Tammuz. Jehovah spoke of what they were doing as being a `detestable thing.' (Ezek. 8:13, 14) According to history, Tammuz was a Babylonian god, and the cross was used as his symbol. From its beginning in the days of Nimrod, Babylon was against Jehovah and an enemy of true worship. (Gen. 10:8-10; Jer. 50:29) So by cherishing the cross, a person is honoring a symbol of worship that is opposed to the true God." - Reasoning From the Scriptures, "Cross"