Skandapurana 1.3.11.59

1.3.11.59

madhyamāṃ varjayitvā tu aṃgulīkdvayena ca..
evaṃ trirekhāsaṃyukto lalāṭe yasya dṛśyate..
sa śaivaḥ śivavajjñeyo darśanātpāpanāśanaḥ.. 13.59 ..

leaving out the middle finger, and using two fingers [as well]. / One who is seen with three lines thus on his forehead / is to be known as a Śaiva, like Śiva himself, destroying sin merely by being seen.