The important part of the answer: every symbol can be redirected for good or for evil, and it all depends on context. You have the power to control your context and thus the choice to make over what symbols you use. In cases like this, where another person's conscience might be affected, Paul gives instructions as to how to make the choice. If you and your friends are strong in faith in God, you are free to use the symbol among them; if you have sufficient concern that some of the public might misinterpret the symbol, you are free to withhold the symbol among them. Unless you have strong evidence (not circumstantial) that Yeti does intend the symbol satanically, you decide the context for yourself.

The first meaning of the longhorn skull, since Yeti is a Texas company, is to affirm the state of Texas (or Aggies). It need not be any more than that. Of course it's true that Virginia O'Keeffe used this symbol on multiple levels, representing both natural beauty and innate sexuality, but that is not the context of this shirt. Of course it's true that goat skulls with two horns are more typically Satanic, but that is not the context of this shirt. Of course some will take anything with two horns as Satanic, but the weakness of their consciences and their inability to see the contextual nuances does not bind your conscience.

Biblically, "two horns" and "pair of horns" symbolize balanced strength and can be used for good or evil. The word "horn" has broad application as in English, and can include the horn of a mountain (summit), a musical horn (trumpet), an ivory horn (tusk), and even a ray of light. Abraham was depicted as having both positive and negative symbology with horns. He found "a ram, caught in a thicket by his horns", a symbol of the Messiah (the powerful one who was yet willingly slain); but he also "defeated the Rephaim in Ashteroth-karnaim", the city of Two-Horned Ashteroth. When Alexander the Great was known as "the two-horned" and when the False Prophet (Revelation 13:11-18) takes up a symbol of a two-horned lamb, they are merely counterfeiting the true power of the Messiah as the Lamb of God. Therefore, you are free to contextualize your shirt as affirming the power of Texas under God. (You are also free to reject it if opposed to your conscience.) In either case, do not bind yourself or another to any certain symbol, word, gesture, or image as necessarily good or evil in itself.