I am trying to create a button which signs the selected .exe file (or better multiple selected files?) with my signtool.exe. This works fine from the command line but not with the button I created:
{filepath} is quoted automatically, if the path contains spaces (unless you add @nofilenamequoting), so adding explicit quotes around it may be resulting in two sets of quotes.
The signtool documentation also says you are missing the sign argument in your command. Are you sure it's exactly the same as what you're running at the command line?