Setting up signed commits on Windows gave me some troubles. In the end, and if you know how, it is straightforward and easy. This is to my future self or other wandering souls.

Disclaimer: This article does not describe setting up / creating GPG keys.

Check your GPG keys

gpg --list-secret-keys --keyid-format LONG

Which gives you a list like the following.

C:/Users/arueckauer/AppData/Roaming/gnupg/pubring.kbx
----------------------------------------------------
sec   rsa4096/E1C0E2DB517C8FBC 2016-07-21 [SC]
      2B30F6F709EF48E6AF669C3FD7EB1106B4940744

uid              [ ultimativ ] Andi Rückauer <arueckauer@example.com>

Setting GPG signing key as configuration setting

git config --global user.signingkey E1C0E2DB517C8FBC

Configure GPG program

git config --global gpg.program "C:\Program Files (x86)\GnuPG\bin\gpg.exe"

Et voilà

Now signing commits should work by passing the -S option with a commit.

git commit -S -m "This is a signed commit"

Further reading