Below are steps to add signatures in Outlook 2013
1. Click on File -> Options.
2. In the Options dialog box, select -> Mail in the list of options on the left side of the dialog box.
3. Click the Signatures button
4. In the Signatures and Stationary dialogue box, you can create new signatures or you can choose exisiting signatures to be your default signature.
5. To create a new signature -> click on New
6. Add your signature in the Edit signature text box.
7. Click on OK.