identifying mark; comradeship mark
A mark used to identify members of a group or to show alliance; often a secret sign among comrades.
They wore red ribbons as an identifying mark.
alignment mark; matching mark
A mark placed on two pieces of material (cloth, wood, etc.) to show where they should be joined or aligned during assembly.
In sewing, you mark alignment marks on the fabric before sewing them together.
A seal or mark used for verification, often in official or commercial contexts; also refers to a tally used for counting or matching. The reading あいいん is a variant for this sense.
See also: 合い印 (あいいん)
They stamp a verification seal to show that the books match the cash.
Standard kanji spelling.
Variant with okurigana.
Rare variant using 標.
Rare variant without okurigana.
Compound of 合い (ai, 'mutual, together') + 印 (shirushi, 'mark, sign'). The exact historical derivation is uncertain, but the word has been used since at least the Edo period for marks of identification and alignment.