Depends what u want to have in there ? If it's an image. Then post it in that box like you post it in a thread --- - Posted using Tapatalk
If you want text, reply to a thread but instead of posting it, copy all the text and paste that into the sig box..... Simples, well that's how I do it, but I'm no expert and I am sure there is a correct way, but I think you need to know BB code, and I only know a little ---