If I got this, (and I'm not saying I do),...Invoices don't need signatures, unless payment is not rendered and/or received by the tax filing deadlines, (from an annual filing point of view, that's where the loss comes in), but when it comes to taxes, invoices allow 1099s to be handled differently, and allow one to do a W4 and receive a W2, otherwise you are a 1099 filer.