diff --git a/IPython/html/notebookapp.py b/IPython/html/notebookapp.py
index 40300f3..51902a2 100644
--- a/IPython/html/notebookapp.py
+++ b/IPython/html/notebookapp.py
@@ -83,13 +83,12 @@ from IPython.kernel.zmq.kernelapp import (
     kernel_flags,
     kernel_aliases,
 )
-from IPython.nbformat import current, sign
 from IPython.utils.importstring import import_item
 from IPython.utils.localinterfaces import localhost
 from IPython.utils import submodule
 from IPython.utils.traitlets import (
     Dict, Unicode, Integer, List, Bool, Bytes,
-    DottedObjectName, Instance,
+    DottedObjectName
 )
 from IPython.utils import py3compat
 from IPython.utils.path import filefind, get_ipython_dir
@@ -218,10 +217,6 @@ class NotebookWebApplication(web.Application):
         return new_handlers
 
 
-#-----------------------------------------------------------------------------
-# Subcommands
-#-----------------------------------------------------------------------------
-
 class NbserverListApp(BaseIPythonApplication):
     
     description="List currently running notebook servers in this profile."
@@ -244,37 +239,6 @@ class NbserverListApp(BaseIPythonApplication):
             else:
                 print(serverinfo['url'], "::", serverinfo['notebook_dir'])
 
-
-class NotebookTrustApp(BaseIPythonApplication):
-    
-    description="""Sign one or more IPython notebooks with your key,
-    to trust their dynamic (HTML, Javascript) output."""
-    
-    examples="""ipython notebook trust mynotebook.ipynb"""
-    
-    notary = Instance(sign.NotebookNotary)
-    def _notary_default(self):
-        return sign.NotebookNotary(parent=self, profile_dir=self.profile_dir)
-    
-    def sign_notebook(self, notebook_path):
-        if not os.path.exists(notebook_path):
-            self.log.error("Notebook missing: %s" % notebook_path)
-            self.exit(1)
-        with io.open(notebook_path, encoding='utf8') as f:
-            nb = current.read(f, 'json')
-        self.notary.sign(nb)
-        with io.open(notebook_path, 'w', encoding='utf8') as f:
-            current.write(nb, f, 'json')
-    
-    def start(self):
-        if not self.extra_args:
-            self.log.critical("Specify at least one notebook to sign.")
-            self.exit(1)
-        
-        for notebook_path in self.extra_args:
-            print("Signing notebook: %s" % notebook_path)
-            self.sign_notebook(notebook_path)
-
 #-----------------------------------------------------------------------------
 # Aliases and Flags
 #-----------------------------------------------------------------------------
@@ -349,7 +313,6 @@ class NotebookApp(BaseIPythonApplication):
     
     subcommands = dict(
         list=(NbserverListApp, NbserverListApp.description.splitlines()[0]),
-        trust=(NotebookTrustApp, NotebookTrustApp.description),
     )
 
     kernel_argv = List(Unicode)
diff --git a/IPython/nbformat/sign.py b/IPython/nbformat/sign.py
index 002242f..4e4feda 100644
--- a/IPython/nbformat/sign.py
+++ b/IPython/nbformat/sign.py
@@ -18,8 +18,11 @@ import io
 import os
 
 from IPython.utils.py3compat import string_types, unicode_type, cast_bytes
-from IPython.config import LoggingConfigurable
 from IPython.utils.traitlets import Instance, Bytes, Enum, Any, Unicode
+from IPython.config import LoggingConfigurable
+from IPython.core.application import BaseIPythonApplication
+
+from .current import read, write
 
 #-----------------------------------------------------------------------------
 # Code
@@ -198,6 +201,41 @@ class NotebookNotary(LoggingConfigurable):
             if not cell.get('trusted', False):
                 return False
         return True
+
+
+class TrustNotebookApp(BaseIPythonApplication):
+    
+    description="""Sign one or more IPython notebooks with your key,
+    to trust their dynamic (HTML, Javascript) output.
     
+    Otherwise, you will have to re-execute the notebook to see output.
+    """
+    
+    examples="""ipython trust mynotebook.ipynb and_this_one.ipynb"""
+    
+    notary = Instance(NotebookNotary)
+    def _notary_default(self):
+        return NotebookNotary(parent=self, profile_dir=self.profile_dir)
+    
+    def sign_notebook(self, notebook_path):
+        if not os.path.exists(notebook_path):
+            self.log.error("Notebook missing: %s" % notebook_path)
+            self.exit(1)
+        with io.open(notebook_path, encoding='utf8') as f:
+            nb = read(f, 'json')
+        if self.notary.check_signature(nb):
+            print("Notebook already signed: %s" % notebook_path)
+        else:
+            print("Signing notebook: %s" % notebook_path)
+            self.notary.sign(nb)
+            with io.open(notebook_path, 'w', encoding='utf8') as f:
+                write(nb, f, 'json')
+    
+    def start(self):
+        if not self.extra_args:
+            self.log.critical("Specify at least one notebook to sign.")
+            self.exit(1)
+        
+        for notebook_path in self.extra_args:
+            self.sign_notebook(notebook_path)
 
-    
\ No newline at end of file
diff --git a/IPython/terminal/ipapp.py b/IPython/terminal/ipapp.py
index 2605e16..4f15d20 100755
--- a/IPython/terminal/ipapp.py
+++ b/IPython/terminal/ipapp.py
@@ -249,6 +249,9 @@ class TerminalIPythonApp(BaseIPythonApplication, InteractiveShellApp):
         nbconvert=('IPython.nbconvert.nbconvertapp.NbConvertApp',
             "Convert notebooks to/from other formats."
         ),
+        trust=('IPython.nbformat.sign.TrustNotebookApp',
+            "Sign notebooks to trust their potentially unsafe contents at load."
+        ),
     ))
 
     # *do* autocreate requested profile, but don't create the config file.