Originally released in 1973 by Tony Orlando and Dawn, this song had a second surge of popularity in 1981 during the Iranian hostage crisis. From Wikipedia I learned It was during the English Civil War that the Puritan Army of English Parliament wore yellow ribbons and yellow sashes onto the battlefield. Yellow became the official color of the armor branch of the U.S. Army. In this song the chorus was a heartfelt plea for remembrance when far away:
Whoa, tie a yellow ribbon 'round the ole oak tree
It's been three long years
Do ya still want me (still want me)
If I don't see a ribbon 'round the ole oak tree
I'll stay on the bus
Forget about us
Put the blame on me
If I don't see a yellow ribbon 'round the ole oak tree
The irony is this yellow ribbon on this tree means the tree is dead and the tag is for the city parks department personnel to remove the tree.
If you're curious, here is a link to the Tony Orlando version of this song: http://tinyurl.com/alhge8h
The song immediately started humming through my head as I read your caption...and then I come to find out the ribbon it there because they'll remove the tree?! No wonder songs don't sound as good today as they did back then!