We present a flexible workflow for the authentication of 3D printed parts and a series of experiments to show that 3D physical signatures extracted from the surfaces of 3D printed parts are able to robustly and uniquely identify and differentiate otherwise identical printed examples. This forms a useful role within the contexts of track-and-trace, product authentication and anti-counterfeiting. It does not require the product itself to be marked in a specific fashion, thus it does not affect the aesthetics or structural integrity of the printed product.