1. Get into the Message window by creating a new email.

2. Click Insert > Signature > Signatures. See screenshot:

By the way, you can also find Message > Signature in the Include group.

3. In the Signatures and Stationery dialog box, select the name of signature you will add a hyperlink to in the Select signature to edit box.
Optional: If you want to create a new signature with hyperlinks, you can click the New button below the Select Signature to edit box. And then type a name for the new signature in the popping up dialog box. See the following screen shot:

4. In the Edit signature section, select and highlight the text you will add a hyperlink for, and click the Hyperlink button in the toolbar. See screenshot:

5. Then the Insert Hyperlink dialog box comes out, please enter the website address in the Address: box, and click OK button.

6. Now you can click the OK button in the Signatures and Stationery dialog box to finish editing.
However, if you want this edited signature with hyperlinks inserted in new messages and Replies / Forwards messages automatically, you have to configure the default signature as follow:

Apply a signature in every new message automatically: In the Choose default signature section, select the signature you want to apply in the New Messages: drop down list.
Apply a signature in every Replies / Forwards message automatically: In the Choose default signature section, select the signature from the drop down list of Replies/forwards:.

Automatically add text and current datetime/timestamps/timezone to subject or signature in Outlook

Provide by Kutools for Outlook.