earmark (n.)

"organ of hearing," Old English eare "ear," from Proto-Germanic *auzon (source also of Old Norse eyra, Danish øre, Old Frisian are, Old Saxon ore, Middle Dutch ore, Dutch oor, Old High German ora, German Ohr, Gothic auso), from PIE *ous- "ear" (source also of Greek ous, Latin auris, Lithuanian ausis, Old Church Slavonic ucho, Old Irish au "ear," Avestan usi "the two ears").

þe harde harte of man, þat lat in godis word atte ton ere & vt atte toþir. [sermon, c. 1250]

In music, "capability to learn and reproduce by hearing," 1520s, hence play by ear (1670s). The belief that itching or burning ears means someone is talking about you is mentioned in Pliny's "Natural History" (77 C.E.). Until at least the 1880s, even some medical men still believed piercing the ear lobes improved one's eyesight. The meaning "handle of a pitcher" is mid-15c. (but compare Old English earde "having a handle," and the image also was in ancient Greek).

To be wet behind the ears "naive" is from 1902, American English. The warning phrase walls have ears is attested from 1610s. French orielle, Spanish oreja are from Latin auricula (Medieval Latin oricula), diminutive of auris.

"trace, impression," Old English mearc (West Saxon), merc (Mercian) "boundary, limit; sign, landmark," from Proto-Germanic *markō (source also of Old Norse merki "boundary, sign," mörk "forest," which often marked a frontier; Old Frisian merke, Gothic marka "boundary, frontier," Dutch merk "mark, brand," German Mark "boundary, boundary land"), from PIE root *merg- "boundary, border." Influenced by, and partly from, Scandinavian cognates. The Germanic word was borrowed widely and early in Romanic (compare marque; march (n.2), marquis).

The primary sense "boundary" had evolved by Old English through "pillar, post, etc. as a sign of a boundary," through "a sign in general," then to "impression or trace forming a sign." Meaning "any visible trace or impression" is recorded by c. 1200. Meaning "a cross or other character made by an illiterate person as a signature" is from late Old English. Sense of "line drawn to indicate the starting point of a race" (as in on your marks ..., which is by 1890) is attested by 1887.

The Middle English sense of "target" (c. 1200) is the notion in marksman and slang sense "victim of a swindle" (1883). The notion of "sign, token" is behind the meaning "a characteristic property, a distinctive feature" (1520s), also that of "numerical award given by a teacher" (by 1829). To make (one's) mark "attain distinction" is by 1847.

In medieval England and in Germany, "a tract of land held in common by a community," hence Mark of Brandenburg, etc.