diff --git a/boards/models/post/sync.py b/boards/models/post/sync.py
--- a/boards/models/post/sync.py
+++ b/boards/models/post/sync.py
@@ -55,62 +55,69 @@ class SyncManager:
 
         models = et.SubElement(response, TAG_MODELS)
 
-        # TODO Put global id's content into XML instad of manual serialization
         for post in model_list:
             model = et.SubElement(models, TAG_MODEL)
             model.set(ATTR_NAME, 'post')
 
-            content_tag = et.SubElement(model, TAG_CONTENT)
-
-            tag_id = et.SubElement(content_tag, TAG_ID)
-            post.global_id.to_xml_element(tag_id)
-
-            title = et.SubElement(content_tag, TAG_TITLE)
-            title.text = post.title
+            global_id = post.global_id
 
-            text = et.SubElement(content_tag, TAG_TEXT)
-            text.text = post.get_sync_text()
-
-            thread = post.get_thread()
-            if post.is_opening():
-                tag_tags = et.SubElement(content_tag, TAG_TAGS)
-                for tag in thread.get_tags():
-                    tag_tag = et.SubElement(tag_tags, TAG_TAG)
-                    tag_tag.text = tag.name
+            if global_id.content:
+                model.append(et.fromstring(global_id.content))
             else:
-                tag_thread = et.SubElement(content_tag, TAG_THREAD)
-                thread_id = et.SubElement(tag_thread, TAG_ID)
-                thread.get_opening_post().global_id.to_xml_element(thread_id)
+                content_tag = et.SubElement(model, TAG_CONTENT)
+
+                tag_id = et.SubElement(content_tag, TAG_ID)
+                global_id.to_xml_element(tag_id)
 
-            pub_time = et.SubElement(content_tag, TAG_PUB_TIME)
-            pub_time.text = str(post.get_pub_time_str())
+                title = et.SubElement(content_tag, TAG_TITLE)
+                title.text = post.title
+
+                text = et.SubElement(content_tag, TAG_TEXT)
+                text.text = post.get_sync_text()
 
-            images = post.images.all()
-            attachments = post.attachments.all()
-            if len(images) > 0 or len(attachments) > 0:
-                attachments_tag = et.SubElement(content_tag, TAG_ATTACHMENTS)
-                attachment_refs = et.SubElement(model, TAG_ATTACHMENT_REFS)
+                thread = post.get_thread()
+                if post.is_opening():
+                    tag_tags = et.SubElement(content_tag, TAG_TAGS)
+                    for tag in thread.get_tags():
+                        tag_tag = et.SubElement(tag_tags, TAG_TAG)
+                        tag_tag.text = tag.name
+                else:
+                    tag_thread = et.SubElement(content_tag, TAG_THREAD)
+                    thread_id = et.SubElement(tag_thread, TAG_ID)
+                    thread.get_opening_post().global_id.to_xml_element(thread_id)
+
+                pub_time = et.SubElement(content_tag, TAG_PUB_TIME)
+                pub_time.text = str(post.get_pub_time_str())
 
-                for image in images:
-                    SyncManager._attachment_to_xml(
-                        attachments_tag, attachment_refs, image.image.file,
-                        image.hash, image.image.url)
-                for file in attachments:
-                    SyncManager._attachment_to_xml(
-                        attachments_tag, attachment_refs, file.file.file,
-                        file.hash, file.file.url)
+                images = post.images.all()
+                attachments = post.attachments.all()
+                if len(images) > 0 or len(attachments) > 0:
+                    attachments_tag = et.SubElement(content_tag, TAG_ATTACHMENTS)
+                    attachment_refs = et.SubElement(model, TAG_ATTACHMENT_REFS)
+
+                    for image in images:
+                        SyncManager._attachment_to_xml(
+                            attachments_tag, attachment_refs, image.image.file,
+                            image.hash, image.image.url)
+                    for file in attachments:
+                        SyncManager._attachment_to_xml(
+                            attachments_tag, attachment_refs, file.file.file,
+                            file.hash, file.file.url)
+
+                global_id.content = et.tostring(content_tag, ENCODING_UNICODE)
+                global_id.save()
 
             signatures_tag = et.SubElement(model, TAG_SIGNATURES)
-            post_signatures = post.global_id.signature_set.all()
+            post_signatures = global_id.signature_set.all()
             if post_signatures:
                 signatures = post_signatures
             else:
-                key = KeyPair.objects.get(public_key=post.global_id.key)
+                key = KeyPair.objects.get(public_key=global_id.key)
                 signature = Signature(
                     key_type=key.key_type,
                     key=key.public_key,
-                    signature=key.sign(et.tostring(content_tag, encoding=ENCODING_UNICODE)),
-                    global_id=post.global_id,
+                    signature=key.sign(global_id.content),
+                    global_id=global_id,
                 )
                 signature.save()
                 signatures = [signature]
@@ -140,8 +147,8 @@ class SyncManager:
                 if exists:
                     print('Post with same ID already exists')
                 else:
-                    global_id.content = et.to_string(tag_content,
-                            ENCODING_UNICODE)
+                    global_id.content = et.tostring(tag_content,
+                                                    ENCODING_UNICODE)
                     global_id.save()
                     for signature in signatures:
                         signature.global_id = global_id
diff --git a/boards/models/signature.py b/boards/models/signature.py
--- a/boards/models/signature.py
+++ b/boards/models/signature.py
@@ -64,6 +64,12 @@ class GlobalIdManager(models.Manager):
 
 
 class GlobalId(models.Model):
+    """
+    Global model ID and cache.
+    Key, key type and local ID make a single global identificator of the model.
+    Content is an XML cache of the model that can be passed along between nodes
+    without manual serialization each time.
+    """
     class Meta:
         app_label = 'boards'
 
diff --git a/boards/signals.py b/boards/signals.py
--- a/boards/signals.py
+++ b/boards/signals.py
@@ -79,3 +79,9 @@ def update_thread_on_delete(instance, **
     thread = instance.get_thread()
     thread.last_edit_time = timezone.now()
     thread.save()
+
+
+@receiver(post_delete, sender=Post)
+def delete_global_id(instance, **kwargs):
+    if instance.global_id and instance.global_id.id:
+        instance.global_id.delete()