This is how to create your own signature that is added automatically to new emails and replies. Note: If signatures are managed centrally in your organization (e.g. with Exclaimer or CodeTwo), don't create your own. Ask support for changes instead.
New Outlook and Outlook on the web
Open Settings (gear) › Accounts or Mail › Signatures.
Choose New signature, enter a name and the text.
Below, choose which signature is used for new messages and for replies/forwards.
Click Save.
Outlook (classic)
Open File › Options › Mail › Signatures ….
Click New, enter a name and the text.
On the right, choose the default signature for New messages and Replies/forwards.
Confirm with OK.
Outlook for Mac
In the menu bar, open Outlook › Settings › Signatures.
Click +, enter name and text and save.
Under Choose default signature, set the signature for new messages and replies.
Outlook app (iPhone and Android)
Tap your profile picture › gear › Signature and enter the text. The app signature only applies on your smartphone.
Tip: Classic Outlook stores the signature only on that computer. New Outlook and Outlook on the web share the signature.