I am filing taxes as head of the household and sending return by mail. Do I need to add my spouse signature to my tax return
No, your spouse does not sign an HOH tax return.
You can only file as HOH if you have lived separately for at least all of the last 6 months of 2016. HOH is designed mainly for single parents and for marital separations, although it can sometimes be used when one spouse is incarcerated or out of the country on military service.
So I am a bit concerned that if your spouse is available and willing to sign the HOH return, you may not meet the requirement that you be living apart. Make sure you really are allowed to file HOH.
The rules and definitions are here https://www.irs.gov/uac/about-publication-501