PitchMark your document(s) every time you pitch to a client.
The Certificate is evidence that you created your material before the date and time of the Certificate.
It has been fitted with a number of security features, to ensure they cannot be forged or copied.
This Certificate is part of the compressed folder containing your other documents. Send the whole compressed folder - including this certificate - to your client.
You are also able to signal to any would-be idea thief that you take your IP seriously, by inserting a badge code into your website gallery, blog or email signature (log in to retrieve the code).
This is what it looks like (click on it to see what happens):