To determine if a tree needs to be cut down, there are several signs to look out for. First, check for any dead or decaying branches, as they can fall and cause damage. Second, look for signs of disease or pest infestations, such as bark that is peeling or discolored, or the presence of insects. Third, consider the tree's location and its proximity to buildings, power lines, or other significant structures. The tree may need to be removed if it poses a risk to safety or property. Additionally, if the tree is leaning heavily or has a large crack in the trunk, it should be inspected by a professional arborist to determine if it needs to be removed.