diff --git a/core/modules/user/src/Tests/UserValidationTest.php b/core/modules/user/src/Tests/UserValidationTest.php
index f5ae202..15a165e 100644
--- a/core/modules/user/src/Tests/UserValidationTest.php
+++ b/core/modules/user/src/Tests/UserValidationTest.php
@@ -133,6 +133,12 @@ function testValidation() {
     $this->assertLengthViolation($user, 'signature', 255);
     $user->set('signature', NULL);
 
+    // Test setting an invalid signature format.
+    $user->set('signature_format', $this->randomString(32));
+    $violations = $user->validate();
+    $this->assertEqual(count($violations), 1, 'Violation found when an invalid signature format is set.');
+    $user->set('signature_format', NULL);
+
     $user->set('timezone', $this->randomString(33));
     $this->assertLengthViolation($user, 'timezone', 32);
     $user->set('timezone', NULL);
diff --git a/core/modules/user/src/UserInterface.php b/core/modules/user/src/UserInterface.php
index 6ccad91..c6f3b2a 100644
--- a/core/modules/user/src/UserInterface.php
+++ b/core/modules/user/src/UserInterface.php
@@ -97,15 +97,12 @@ public function setEmail($mail);
   public function getSignature();
 
   /**
-   * Set the user signature.
-   *
-   * @todo: Convert this to a configurable field.
+   * Sets the user signature.
    *
    * @param string $signature
    *   The new signature text of the user.
    *
-   * @return \Drupal\user\UserInterface
-   *   The called user entity.
+   * @return $this
    */
   public function setSignature($signature);
 
@@ -118,13 +115,12 @@ public function setSignature($signature);
   public function getSignatureFormat();
 
   /**
-   * Set the signature format.
+   * Sets the signature format.
    *
-   * @param string
+   * @param string $signature_format
    *   The name of the new filter format.
    *
-   * @return \Drupal\user\UserInterface
-   *   The called user entity.
+   * @return $this
    */
   public function setSignatureFormat($signature_format);