大毘盧遮那成佛經疏 13.209

13.209

次發生佛頂，作蓮華印（即前觀音印也）。無量音聲佛頂，作商佉印，如前說（謂三補吒，雙屈二空以風並壓之）。

Next, for the Mahodayoṣṇīṣa, make the lotus mudrā (that is, the previous Avalokiteśvara mudrā). For the Anantasvaroṣṇīṣa, make the śaṅkha mudrā as previously explained (that is, form a saṃpuṭa, bend both space fingers, and press them with both wind fingers).