Sales Complete

What to do when a client has said yes, has the contract, and just has not signed it. I panic. Maybe that is not the right process, but I indeed panic that the deal is not done. I have waited for three weeks for a client to just sign the documents. I cannot proceed until they are signed. They have said they want to do it, are excited, but have not completed the work. I don't know what to do. I do not want to be overbearing, but I want them to know it is priority. I have sent an email reminder and talked to them on the phone, but wanted to give it a couple days before I moved forward with anything. I guess today my lesson is patience.