Having a new hire sign their offer letter to signify their commitment to accept the offer made is a great idea. It is very critical, though, that your offer letter state that the employment is at-will and that the document is not intended to be a contract, either written or implied. With these key statements present, the signature in most cases is just a symbolic acceptance of the role and the terms of employment, still leaving the employer with a fair amount of leeway to operate. Beyond that, the legal value is minimal, at best. In fact, the reason to have a signature from your new hire is more about making them think they have made a commitment in writing, thereby reducing the possibility of them accepting another job or even a counteroffer.