In Outlook 2013 Inbox window, click "New E-mail" icon under "Home" tab.
The new message window pops up, under the "Message" tab, in the "Include" group, click the "Signature" icon, and then select "Signatures..." from the drop down menu.
The "Signature and Stationery" window pops up, there are three sections under E-mail Signature tab:
In "Select signature to edit" section, click "New" button.
You'll be asked to name this signature, give a name, then click "OK"
In "Edit signature" section, type in the text for your new signature and format it in any way you want, then click "Save" button above it (right beside the "New" button).
In "Choose default signature" section:
To create another signature, repeat step 1-3.
Click "OK" to close the "Signature and Stationery" window.
Next time when you write a new email message, the default signature will automatically be included if you have set it up in step 3, otherwise, you can click the "Signature" icon and select one from the list: