There isn't, but remember, the whole point of signing something is to put it out there in the open. If an employee grabs older work, signs it with his personal-

There isn't, but remember, the whole point of signing something is to put it out there in the open. If an employee grabs older work, signs it with his personal-project key, and then tried to sue the employer for using code which belonged to him, then the employer could easily show a court the timestamps/logs which prove that the code was originally signed over to the employer and thus belonged to the employer under contract. And if the employee is secretly signing work with his own key over time before signing it with the employer's certificate, then his own record of ownership will be in parallel to the employer's record of ownership, thus proving that the work belongs to the employer under contract. The whole point is how to distinguish work that the employee is not signing over to the employer at all - because it's originally a personal project. Then the employer will have no record of the code being signed over to the employer, and the proof clearly shows the code belonging to the employee.