You can hear the song from miles away. The song is enchanting in a mild way. Even the plants sing this haunting tune all day. This gives you fair warning to be ready to dance to a different tune. You are leaving your country and entering theirs.
This relic, while of little value against the living, is a formidable tool against the beasts from beyond.
The D’athri took to space in such a way to make Terrans look "gun shy". They can be found in small numbers in and around every space port in Known Space.
(Apologies to GRRM and HBO)
A group of northerners want to bring the Old Gods back to the south. They grow cuttings from the white trees seeking the blessings of the Old Gods on the project, and when the saplings are big enough, they carve faces in them and secretly plant them in forests all over the south, to extend the 'reach' of the Old Gods.
The plan works of course, but the trees are *baby gods*, and behave as such when invoked.