If your CRM is using windows authentication to login and does not ask for credentials while getting in, then you will not get Log out button. you need to change your CRM URL from Local Intranet zone to Internet zone so that you will have credential pop
up enabled while logging in and log out button is enabled.
If my response answered your question, please "mark the response as an answer" and also "vote as helpful". Regards, Hari. www.crm2011byhari.blogspot.com