There are actually three different lichens here - growing on silver leaf maple bark. Green shield lichen is the obvious one. Then, to the left and toward the bottom, the dark brown splotchy patch is script lichen - so named because it can look like ancient writing. Last, at top and about center are black spots - dot lichen. Scientists use lichen growth and health to determine the quality of the air we breathe. So learn to like your lichens! I've read that you can eat lichens - but that they don't taste very good.
Green Shield Lichen info can be found on page 24 of the Franz Lichen Guide. Script Lichen info is located on page 48. There are so many dot lichens, I couldn't begin to tell you which one it is without a microscope. The guide is available as a free download in PDF format. Just google it, if you're interested in learning about lichens where you live.
