Previous research employing a conceptual approach with a digital twin has demonstrated that (noise-based) dynamic watermarking is incapable of providing unconditional security in smart electrical grid systems. However, the implementation of digital twins can be prohibitively costly or infeasible due to limited available data on critical infrastructure. In this study, we first analyze the spectral properties of dynamic watermarking and its associated protocol. Subsequently, we present a straightforward attack inspired by the digital twin method, which extracts and utilizes the grid noises and completely breaches the security of dynamic watermarking without requiring knowledge of the private watermarking signal. The attacker can fully expose the grid while evading detection by the controller. Our findings indicate that in the absence of secure and authenticated communications, dynamic watermarking offers neither conditional nor unconditional security. Conversely, when communication lines, sensors, and communicators are equipped with tamper-resistant and secure/authenticated links, dynamic watermarking becomes redundant for grid security.