Vaishnava Dharmashastra 7.12

7.12

varṇaiś ca tatkṛtaiś cihnaiḥ patrair eva ca yuktibhiḥ
saṃdigdhaṃ sādhayel lekhyaṃ tadyuktipratirūpitaiḥ //

If the authenticity of a document is contested, it should be ascertained by (comparing with it other) letters or signs (such as the flourish denoting the word Srî and the like) or documents executed by the same man, by (enquiring into) the probabilities of the case, and by (finding out such writings as show) a mode of writing similar (to that contained in the disputed document).