Hello Jim,

Unfortunately, this is not a good sign. These are wood-decay fungi, and indicate that the interior wood of the trunk has been decaying for some time. (The fungal "mushrooms" don't appear until the growth of the fungus is fairly advanced.) While the innermost trunk tissues can decay with minimal impact on the tree's health, other tissues just beneath the bark are vital to the tree's survival. In either case, there is no action you can take at this point; it cannot be treated with fungicides to reverse the damage, nor will the tree regrow what the fungus has degraded.

We suggest you consult with a certified arborist who can assess the tree in person. While they probably can't take any actions to remediate the tree's decline, they should be able to determine how much of a fall or breakage risk/hazard the tree poses in its current state. Since a structural failure would probably damage property and risk harming people, given the tree's location, they will likely recommend it be removed for safety. If the person recommends costly treatments, you can always seek a second opinion from another arborist. Some arborists work as employees of tree-care companies while others consult independently.

Miri