This specification discloses non-aqueous solvent, pigmented ink formulations that are suitable for the electronic and aerospace industries and form printed marks that are resistant to smearing and dissolution by organic solvents commonly used in overcoatings in this industry and others. These ink formulations are based on use of an acidic resin with an inherent acid value of at least about 25 mg KOH/g, preferably at least partially neutralized by a quaternary ammonium hydroxide and/or alcohol amine acid neutralizing or modifying agent.