11. Starship Emblems
Not every ship in Starfleet used the delta symbol that is associated with Star Trek today. The crews of the different ships had different emblems on their uniforms as a way of signifying which ship they served on. Episodes like The Doomsday Machine and The Ultimate Computer are excellent examples of the variety of starship emblems.
However, in future series, virtually everything associated with Starfleet used the delta symbol that was originally just reserved for the Enterprise. While this could be viewed as a natural change in Starfleet's logo design, everyone uses the same delta symbol even in the prequel shows. There is no indication that other ships, past or future, ever use their own emblems again.