app/views/shared/_banner.html.erb
<%- if ENV["BANNER_HTML"].present? && session[:banner_viewed].blank? -%>
<div class="banner">
<div class="banner-content">
<a href="#" class="banner-close"><i class="icon-remove"></i></a>
<div class="banner-header">
<%= raw(ENV["BANNER_HTML"]) %>
</div>
</div>
</div>
<% session[:banner_viewed] = true %>
<%- end %>