Automatically insert email signature into Outlook Meeting Invite

Outlook 2010 and newer include the form designer.

File -> Options -> Customize Ribbon, then, in the Right Side pane, click to turn on the Developer Tab.

From there you can design Meeting Request template to your specification.

Then, to use it, you will select:

New -> Meeting Request Using -> (Your Custom Template) from the Outlook Home tab.

You can handle the ItemSend event of the Application class where you can check out the message class of the outcoming Outlook item and change the message body if required.

Think you will find the Getting Started with VBA in Outlook 2010 article helpful.