Carbon dots (CDs) with excellent fluorescent performance are a potential material to restrain fakes, but the complex processes, high cost, and toxicity impede their application. Here, Lycium ruthenicum is employed as the carbon source, and eco-friendly CDs are obtained via a one-step hydrothermal method. The reaction conditions such as dosage, temperature, and time are optimized to achieve high yield, and the morphology, surface functional groups, and optical properties are characterized by scientific instruments. The results show that the spherical CDs with a diameter of 1.83 ± 0.30 nm have excellent solubility and a strong absorption peak at 285 nm. Subsequently, CDs were made into fluorescent inks; an ink-jet printer and a fountain pen are selected to examine the anti-counterfeit effect. Notably, the encrypted patterns can be hidden and perceived easily under natural light and UV light. Hence, these prepared CDs are expected to be an alternative material to be applied in the security field.