You can find the External TF card and USB Storage in the/mnt/media_rw directory.
You can also refer to the demo that explains how to access them here:
http://github.com/leavs/WRFileDemo.git
Check http://github.com/leavs/WRFileDemo.git to learn how to use them.
For the signatures Tools, please download them from the following link:
http://chipsee-tmp.s3.amazonaws.com/Tools/imx6_android6.0_security.zip