What is the meaning of Dhamma-lakkhaṇa?
“法印”是什么？

Lakkhaṇa means mark or seal. An imperial seal certifies the authenticity of documents, allowing for passage without hindrance. Here, it is used in analogy for the principal doctrines of Buddhism. If any doctrine is in line with the "Seals of Dhamma", it can be regarded as authentic teaching of the Buddha. (If it has been mastered, all Dhammas will be grasped without obstruction.) That is why they are called the "Seals of Dhamma". If, after "All phenomena are impermanent, all dhammas are devoid of self", we add "Nibbāna is serene", we have what are called the Three Seals of the Dhamma. With the addition of "All defiled (sāsava) dhammas lead to suffering", we have the Four Seals of Dhamma.
印就是印玺。国王的印玺可以证明文件的真实（有通行无阻的作用）。借以比喻佛教的主要教义，也以符合“法印”而证明其为真正佛法（掌握了它，便能对一切法通达无碍），所以称为法印。“诸行无常，诸法无我，涅槃寂静”，并称三法印，或者加上“有漏皆苦”，亦称四法印。