Someone spray painted our tree.. can we cover it up?

the best way would to let Mother Nature wear it off. I doubt the trees was primed befor painting or cleaned. . The next question, the tree in your yard or on the parking? If tree roots are getting into the sewer...the city may have marked it for removal.

I am so sorry to hear that. How awful. Here is a link that might help you. I wish you luck.

https://www.extension.purdue.edu/extmedia/fnr/fnr-474-w.pdf

I would just try to get a color the same as the bark on your tree and just test a little area to see if it affects the tree or not, before I paint the whole trunk. Also you might want to check with your extension agency to see if that is safe.

In our city, if a tree is to be taken down due to the many different problems trees are having lately, they put a red X on it and a sign from the city, until the paper that is stapled blows off. If it is on the boulevard, it may have been marked for removal, but usually it is just a single mark, like ours is an X. If it isn't the city or county taking it down, just let the weather do its job, it probably isn't covered enough to hurt it.

How horrible! Do you have security cameras? How much of the tree was painted? I would call in an arborist to determine what to do. Painting tree trunks can kill a tree if left untreated.

https://www.gardenguides.com/127387-remove-paint-vandalized-trees.html