That's what the term "tag" is refering to; just as the graffiti artist has his "tag" (an image or design to distinguish himself), so does the digital artist. As far as I'm concerned a signature is the space below one's post reserved for w/e the user wants to put there, and a tag is a user made image which is put in the signature. The name has no indication of the tools used.
I agree with some people here, tag sounds a bit more professional, like most of the sig makers here. Sigs are just gfx thrown together I guess.
Something along the lines of what I was thinking. If I lay down a "tag" or "bomb" (<--- to be proper) then that's what I think when I here people referring to "sigs" as "tags. If you know what I mean. Sig. Why change something that 90% of people know what it is rather than claling it a Tag?
i kno they the same but i feel its more appropriate like TAG=a sig which is wider then it is tall SIG=a more squarish shape to it