There is no such function in Excel and to workaround this problem you have two options:
Here, I’ll discuss first option.
One of many wrongs, fuckups and things that are missing in Microsoft Outlook is the fact that you can’t set default signature for every new calendar meeting invitation, as you’d do for any new email message.
Things gets even worse as you dig through the problem and realize that Outlook developers were stupid enough to force you to design a whole new meeting template instead of just giving you an option to enable or disable this feature (as — again — it works in case of emails).
This guide is a redesigned version of this Stack Overflow answer (or actually this comment).
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