Arborglyphs

Carving names and initials into trees is a common practise, particularly among lovers;
The carvings can last for decades, as a symbol of the permanence of the couple's ardour,
or in the case of the commonly more lewd carvings, a testament to the snail's pace at which man's civility develops.
This practise would appear to date back up to the Classical era, with Callimachus writing in his Aetia,

"But graven on your bark may ye bear such writing as shall declare "Cydippe beautiful".

It also appears in the Eclogues of Virgil:

"Resolved am I in the woods, rather, with wild beasts to couch, and bear my doom,
and character my love upon the tender tree-trunks: they will grow, and you, my love, grow with them."

This carving was also practised in Renaissance England, as evidenced by the writings of William Shakespeare (in 'As You Like It', 1599).