Vaisesika Sūtra 2.1.8

viṣāṇī kukudvān prāntēvāladhiḥ sāsnāvān iti gōtvē druṣṭaṁ liṅgam ॥8॥

Poison of the scorpion, rabbit dwelling on the outskirts, cow-ness of the cow - are the visible distinguishing marks.