Redmine

It's only necessary to edit app/views/users/show.html.erb

And just after :

  <% unless @user.pref.hide_mail %>
    <li><%=l(:field_mail)%>: <%= mail_to(h(@user.mail), nil, :encode => 'javascript') %></li>
  <% end %>

Add :

  <% if User.current.admin? %>
    <li><%=l(:field_login)%>: <%= h(@user.login) %></li>
  <% end -%>