<% if user_signed_in? %>
  <li>
  <%= link_to('Logout', destroy_user_session_path, :method => :delete) %>
  </li>
<% else %>
  <li>
  <%= link_to('Login', new_user_session_path)  %>
  </li>
<% end %>

<% if user_signed_in? %>
  <li>
  <%= link_to("Logout #{current_user.email}", destroy_user_session_path, :method => :delete) %>
  </li>
<% else %>
  <li>
  <%= link_to('Login', new_user_session_path)  %>
  </li>
<% end %>

Add current_user.email to Logout link text.
Add current_user.email to Logout link text.
