insignia (n.)

early 13c., signe, "gesture or motion of the hand," especially one meant to express thought or convey an idea, from Old French signe "sign, mark," from Latin signum "identifying mark, token, indication, symbol; proof; military standard, ensign; a signal, an omen; sign in the heavens, constellation."

According to Watkins, literally "standard that one follows," from PIE *sekw-no-, from root *sekw- (1) "to follow." De Vaan has it from PIE *sekh-no- "cut," from PIE root *sek- "to cut" He writes: "The etymological appurtenance to seco 'to cut' implies a semantic shift of *sek-no- 'what is cut out', 'carved out' > 'sign'." But he also also compares Hebrew sakkin, Aramaic sakkin "slaughtering-knife," and mentions a theory that "both words are probably borrowed from an unknown third source."

It has ousted native token. By c. 1300 as "an indication of some coming event." The meaning "a visible mark or device having some special meaning" is recorded from late 13c.; that of "miraculous manifestation, a miracle demonstrating divine power" is from c. 1300. In reference to one of the 12 divisions of the zodiac, from mid-14c.

The sense of "inscribed board with a characteristic device attached to the front of an inn, shop, etc.," to distinguish it from others is recorded from mid-15c. The meaning "indicator, token or signal of some condition" (late 13c.) is behind sign of the times (1520s). The meaning "conventional mark or symbol in place of words" (in music, mathematics, etc., as in plus sign) is by 1550s. In some uses, the word probably is a shortening of ensign. 

early 15c., "a token, sign, symbol; badge of office, mark or insignia of authority or rank;" also "battle flag, flag or banner of a ship or troop of soldiers," via Scottish, from Old French enseigne (12c.) "mark, symbol, signal; flag, standard, pennant," from Latin insignia (plural); see insignia, which is a doublet of this word. As the word for the soldier who carries the flag, 1510s. U.S. Navy sense of "commissioned officer of the lowest rank" is from 1862. French navy had rank of enseigne de vaisseau at least since early 18c. Until 1871 one of the lowest grades of commissioned officers in a British army infantry regiment, also a rank in the American Revolutionary army.

Proto-Indo-European root meaning "in."

It forms all or part of: and; atoll; dysentery; embargo; embarrass; embryo; empire; employ; en- (1) "in; into;" en- (2) "near, at, in, on, within;" enclave; endo-; enema; engine; enoptomancy; enter; enteric; enteritis; entero-; entice; ento-; entrails; envoy; envy; episode; esoteric; imbroglio; immolate; immure; impede; impend; impetus; important; impostor; impresario; impromptu; in; in- (2) "into, in, on, upon;" inchoate; incite; increase; inculcate; incumbent; industry; indigence; inflict; ingenuous; ingest; inly; inmost; inn; innate; inner; innuendo; inoculate; insignia; instant; intaglio; inter-; interim; interior; intern; internal; intestine; intimate (adj.) "closely acquainted, very familiar;" intra-; intricate; intrinsic; intro-; introduce; introduction; introit; introspect; invert; mesentery.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit antara- "interior;" Greek en "in," eis "into," endon "within;" Latin in "in, into," intro "inward," intra "inside, within;" Old Irish in, Welsh yn, Old Church Slavonic on-, Old English in "in, into," inne "within, inside."