If you Earmark something you intend to set it aside for yourself. The word's origin is found in the ancient art of marking cattle ears with a ring or a tab. Owners would tag their cattle and potential owners at market would set cattle aside in this way, indicating their intention to buy. And centuries before this, the practice even included human property: slaves would have "their ears borne through with an awl" to distinguish ownership. Out of this practice came the later fashion of wearing earrings. In relatively recent times the word spread into wider use.