At present, the economic loss caused by the forgery of ink marks is increasing annually. This study presents a method for identifying ink marks using swept source optical coherence tomography (SSOCT). To acquire the back-scattered light intensity from ink marks written on white paper, a custom-built SSOCT system was used. The attenuation coefficient of each ink mark was obtained by data fitting, which was used to distinguish ink marks written with different brands of ink of the same color. Experiments show that the attenuation coefficient of PILOT ink, Deli ink, and Hero ink is in the range of 0.1333--0.1434, 0.1501--0.1695, and 0.1748--0.1892, respectively. We reconstructed X-Y cross-sectional images of characters written using different brands of ink. The ink marks can be distinguished successfully by the proposed method, which validates its feasibility.