/in sig"nee euh/ , n., formally a pl. of insigne , but usually used as a sing. with pl. insignia or insignias .
1. a badge or distinguishing mark of office or honor: a military insignia.
2. a distinguishing mark or sign of anything: an insignia of mourning.
Also, insigne .
[ 1640-50; insigne mark, badge, n. use of neut. of insignis distinguished (by a mark); see IN- 2 , SIGN ]
Usage . INSIGNIA, originally the plural of Latin insigne, began to be used as a singular in the 18th century, and the plural INSIGNIAS appeared shortly thereafter. All uses - INSIGNIA as a singular or plural and INSIGNIAS as a plural - are fully standard. The singular INSIGNE still occurs, but INSIGNIA is more common.