Yes, a good sign! Tried to paste some info and a link in earlier but couldn't.
"Algae, lichens and moss are non-parasitic plant-like organisms that colonise bark, rock and other hard surfaces. Lichens and algae are often mistaken for a fungal disease but, fortunately, they do not harm plants on which they grow. Furthermore, they can give a mature look to a garden, preferring damp areas with minimal air movement."
"However, growths of algae, lichens and moss may be more common on plants lacking vigour, so their presence could indicate that attention is needed, particularly on old fruit trees and azaleas."
You'll know more when you see how it flowers. But any shrub or tree does better when it's not competing with grass/lawn. So if you're at all worried I'd be removing it and mulching round the base of the tree.