**** UPDATE ****

Thanks Burt for the comment pointing out that the original code I posted is actually deprecated and for pointing out a better way for testing environment.

According to the docs (and Burt), this is the correct way to test for environment in a GSP.

<g:if env="production">
    <!-- Markup to include ONLY when in production -->
</g:if>

**** The code below is deprecated ****

<g:if test="${ grails.util.GrailsUtil.getEnvironment().equals(org.codehaus.groovy.grails.commons.GrailsApplication.ENV_PRODUCTION) }">
	<!-- Markup to include ONLY when in production -->
</g:if>

Hope this helps others who are looking to do the same within their GSPs.