अमुद्राणामत्ययो देयद्विगुणः ॥ कZ_०२.२१.०३ ॥
amudrāṇām atyayo deyadviguṇaḥ
For goods without an official seal, the penalty (for the offence) shall be twice the amount due.
It makes evasion economically irrational by making the expected cost exceed the avoided duty, while still being administratively simple to compute.