This is pretty easy and there's already an example of it a few places within the default design. Use the following Smarty code:
{if not $logged_in} {*Logged out code*} <!-- any html/smarty code you want to display when logged IN to your Geo software --> You are logged in {else} {*Logged in code*} <!-- any html/smarty code you want to display when logged OUT your Geo software --> You are logged out {/if}
You can choose to display something only when logged in or only when logged out and do nothing with the "other side". Many want a login form within specific templates but don't want to display a login form when you are already logged into the site. This helps with that and many other things to fit your needs.