Visual Studio isn't signing bits for me.

Just use the command line tool to get going.

sign.sh

@@ -0,0 +1,8 @@
+#!/bin/bash -ex
+export "PATH=$PATH:/cygdrive/c/Program Files/Windows Kits/8.1/bin/x86"
+for f in Release Debug;
+do
+  signtool sign /f winsw_cert.pfx /t http://timestamp.verisign.com/scripts/timestamp.dll bin/$f/winsw.exe
+  signtool verify /v /pa bin/$f/winsw.exe
+done
+echo success

winsw.csproj

@@ -15,7 +15,7 @@
     <StartupObject>
     </StartupObject>
     <SignManifests>false</SignManifests>
-    <SignAssembly>true</SignAssembly>
+    <SignAssembly>false</SignAssembly>
     <AssemblyOriginatorKeyFile>winsw_cert.pfx</AssemblyOriginatorKeyFile>
     <FileUpgradeFlags>
     </FileUpgradeFlags>