<Dashboard> or <CallButtons> ... <Button> <title>Sign Out</title> <action>SIGNOUT_CHANGE</action> <value></value> <enabled>true</enabled> <confirm>false</confirm> <description></description> <icon></icon> <scale>CENTER_INSIDE</scale> </Button> ... </Dashboard> or </CallButtons>
$ adb shell am broadcast -a wfc.voice.SIGN_OUT