During the late 60's, an unknown actor entered the small, but highly interesting field of hyper-travelling sub-particles. This new actor, who was active mainly in the mainland US - became known as Delta Sigma. The identity of this actor - known primarily for always leaving a signature consisting of the the signs for Delta and Sigma - at every visited dimension.
When other travellers, upon arriving in the visited dimension, found this inter-galactic hyper-graffiti - they named is after the traveller who first found it and documented it, namely James Tagleft. The signatures become known as Tags.