This patch solves https://savannah.gnu.org/bugs/index.php?52002


--- a/util/grub-mkconfig_lib.in
+++ b/util/grub-mkconfig_lib.in
@@ -188,6 +188,7 @@
       *.dpkg-*) return 1 ;; # debian dpkg
       *.rpmsave|*.rpmnew) return 1 ;;
       README*|*/README*)  return 1 ;; # documentation
+      *.sig) return 1 ;; # signatures
     esac
   else
     return 1