The crossword solution for the term SIGN, AS A DEAL is INK. INK is a liquid or paste that contains pigments or dyes and is used to color a surface to produce an image, text, or design. It is most commonly used for writing, drawing, and printing. INK is also used in the production of documents, photographs, and other artwork. In some cases, it is even used to create tattoos. INK is an essential tool for signing documents, as it is a permanent and visible way to signify agreement.