bookmark (n.)

Middle English bok, from Old English boc "book, writing, written document," generally referred (despite phonetic difficulties) to Proto-Germanic *bōk(ō)-, from *bokiz "beech" (source also of German Buch "book" Buche "beech;" see beech), the notion being of beechwood tablets on which runes were inscribed; but it may be from the tree itself (people still carve initials in them).

Latin and Sanskrit also have words for "writing" that are based on tree names ("birch" and "ash," respectively). And compare French livre "book," from Latin librum, originally "the inner bark of trees" (see library).

The sense gradually narrowed by early Middle English to "a written work covering many pages fastened together and bound," also "a literary composition" in any form, of however many volumes. Later also "bound pages," whether written on or not. In 19c. it also could mean "a magazine;" in 20c., a telephone directory.

The use of books or written charters was introduced in Anglo-Saxon times by the ecclesiastics, as affording more permanent and satisfactory evidence of a grant or conveyance of land than the symbolical or actual delivery of possession before witnesses, which was the method then in vogue. [Century Dictionary] 

From c. 1200 as "a main subdivision of a larger work." The meaning "libretto of an opera" is from 1768. A betting book "record of bets made" is from 1812. The meaning "sum of criminal charges" is from 1926, hence slang phrase throw the book at (1932). Book of Life "the roll of those chosen for eternal life" is from mid-14c. Book of the month is from 1926. To do something by the book "according to the rules" is from 1590s.

"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.