verification seal; tally mark
A mark or seal used to verify that two items match or belong together, often by aligning halves of a stamp or seal across two documents or objects.
I stamp a verification seal on the contract.
割符には合い印が付けられている。
A tally mark is placed on the tally stick.
Standard kanji spelling.
Variant spelling without the okurigana い.
Compound of 合い (ai, 'matching') + 印 (in, 'mark' or 'seal'). The exact historical derivation is uncertain, but the word has been used since at least the Edo period for verification marks.