also: しょうとして
expression
as proof of; as a sign of; in token of
Used to indicate that something serves as evidence, a token, or a demonstration of a feeling, fact, or commitment. Often appears in formal or written contexts.
感謝の証として、ささやかな贈り物をお送りします。
As a token of our gratitude, we are sending you a small gift.
彼は友情の証として、その指輪を私にくれた。
He gave me the ring as a sign of our friendship.
From 証 (あかし, 'proof, evidence') + として ('as'). The reading しょうとして is a Sino-Japanese variant, less common in everyday speech.