This question has been answered by shonna. See the first response.
[[!+modx.user.id:if=`[[!+modx.user.id]]`:eq:=`0`:then=`Not logged in. <a href="[[~123]]">Login</a>`:else=`Welcome [[!+modx.user.username]]`]]
the same thing is happening. Btw there was a ? and ! because it's supposed to read like this:[[!Personalize? &yesChunk=`Logout` &noChunk=`Login_Box`]]
<div id="topnav" class="topnav"><a href="[[~76]]" class="signin"><span>Login </span></a> </div>
<a href="[[~76? &service=`logout`]]" title="Logout">Logout</a>
[[!Profile]] <p>Hello [[+fullname]]</p>