This two-page letter is from 2012. It remains unclear who it was addressed to and appears to be from the Department of Veterans Affairs.
It states on page two that "a determination of incompetency will prohibit you from purchasing, possessing, receiving, or transporting a firearm or ammunition. If you knowingly violate any of these prohibitions, you may be fined, imprisoned or both pursuant to the Brady Handgun Violence Prevention Act, Pub I, No. 103-159, as implemented at 18, United States Code 924(a)(2)."