A file to protect your lien rights has different names in different states but no matter what the document is called, you should obtain one to protect your lien rights. If your state does not offer one, you should file for a preliminary notice on every job that allows you to do so.
One mistake that contractors make is forgetting that this is a business, not a relationship, and trusting their client so much that they feel they do not need to do this. Obtaining this type of document simply lets your client know that you are protecting your right be paid for the project:
Maintaining your lien rights, and following through with a lien when necessary, demonstrates that you're a professional. You run your business like a business and expect to be paid accordingly. It also sends a message to everyone concerned that your company won't play games when it comes time to be paid for the work completed.