You have to put loads of seperate colours for each letter i think.

Yeah I tried that but it doesnt look good

You won't be able to have more than three or four rainbowish words in your signature due to limitations.

How do I do it I only want to Write -Demon|Origin

I think that still will be too much code, but you can try I guess.

[color=#ff0000]-[/color][color=#eb3a13]D[/color][color=#d77127]e[/color][color=#c4a23a]m[/color][color=#b0cb4e]o[/color][color=#9ce962]n[/color][color=#89fa75]|[/color][color=#75fe89]O[/color][color=#62f59c]r[/color][color=#4edfb0]i[/color][color=#3abcc4]g[/color][color=#2790d7]i[/color][color=#135ceb]n[/color]

Thanks too much code but atleast i fit in Demon haha