Hello,
I'd like to understand once for all and share with you what I learned during my tests about Outlook signatures and registry settings.

When a user create and then set signature for new messages and replies, the information are stored by Outlook under registry keys New Signature and Reply-Forward Signature (REG_BINARY) respectively. A good explanation here Configuring Outlook for the signatures within the users registry.
The registry path depends on Outlook version:

Outlook 2007, 2010

HKCU\Software\Microsoft\Windows NT\CurrentVersion\Windows Messaging Subsystem\Profiles\<Profile Name>\9375CFF0413111d3B88A00104B2A6676\<0000000x>

Outlook 2013

HKCU\Software\Microsoft\Office\15.0\Outlook\Profiles\<Profile Name>\9375CFF0413111d3B88A00104B2A6676\<0000000x>

Now, If you don't want users be able to change their signature from Outlook (options grayed out), it's necessary to set registry keys NewSignature, ReplySignature (REG_SZ). A good explanation here Disable End-User's Ability to Add, Edit, & Remove Outlook Signatures.
The path where they are is this:

HKCU\Software\Microsoft\Office\<Version>\Common\MailSettings

But what is written on this Microsoft KB How to deploy a default email signature in Outlook is little bit different (below point 6):

"...By using these steps, the specified signature will automatically appear in new e-mail messages (and optionally, replies to e-mail messages). However, users are still able to manually edit or remove these default signatures. ..."

That isn't true because, as written above, if both registry keys NewSignature and ReplySignature are set the option are grayed out and users cannot change signature from Outlook.

Note: If registry key First-Run is deleted, after Outlook has been started, then it is being added back again and the NewSignature and ReplySignature values are automatically being removed, and users are able to change their signature from Outlook. A good explanation here Setting up a Corporate Signature (source HowTo-Outlook).
This is the path where registry key is stored:

HKCU\Software\Microsoft\Office\<Version>\Outlook\Setup

What about ? Are all these information right ? Is there an error on Microsoft KB ?

Thank you very much,
Luca

Hi Luca,

The Microsoft KB article is correct. According to my testing. the registry keys NewSignature and ReplySignature won't make the signatures option grayed out, they only change the default email signatures when composing a message or replying a message.

Regards,

Steve Fan
TechNet Community Support

Hello Steve,
I'm sorry but I don't agree with you totally: if you set NewSignature and ReplySignature and you never started MS Outlook before or you removed HKCU\Software\Microsoft\Office\<Version>\Outlook\Setup\First-Run key, then they are set as default only (no options grayed out). But if latest registry key is already present, then options are grayed out.

If you don't agree with me, then, answer to this: if NewSignature and ReplySignature won't make the signatures option grayed out, then what are registry keys to set options grayed out ?

Bye,

I'm seeing the same behavior.

Did you ever solve this issue?

Hello Elan,
you can manage it as you prefer (refer to first post).
I wrote this post to know if Microsoft KB was wrong or not (because I experienced a different behavior).

What's your objective ?

Bye,
Luca

I can confirm Luca's comment about the NewSignature, ReplySignature and First-Run keys. If the first two are set to anything, and First-Run is missing, all the buttons for Signatures are disabled.