Add a copyright header to the all your source files, with PowerShell.

gistfile1.txt

# Create a file `~\header.cs` with the copyright or whatever you want
# in each file. Then run this script.
#
# Notes:
#
# Second step will force BOM at the start, and newline at the end, of each 
# file. It will also push all file encodings to be the same. Those make 
# diffs a little ugly.
#
# So, I do it in two steps: one to normalize encoding, and one to actually
# insert the header.
#

$encoding = "utf8"      # change this if step 1 produces wacky, unexpected results results
$pattern = "*.cs"       # files you want to change.

gci -Recurse -Include $pattern -File | 
    % { 
        cp $_.FullName ~/temp -Force
        gc ~/temp | Out-File $_.FullName -Encoding $encoding
    }

git gui     # review, and commit

gci -Recurse -Include $pattern -File | 
    % { 
        cp $_.FullName ~/temp -Force
        cat ~/header.cs | Out-File $_.FullName -Encoding $encoding
        gc ~/temp | Out-File $_.FullName -Encoding $encoding -Append
    }

git gui     # review, and commit