I am using the API service and I was attempting to fetch
/data/wow/search/media?namespace=static-us&tags=guild-crest&orderby=id&_page=1&access_token=YOURACCESSTOKENHERE
and this gets nothing. Out of the following tags("achievement", "creature-display", "creature-family", "guild-crest", "item", "keystone-affix", "pet", "pet-ability", "playable-class", "playable-specialization", "profession", "pvp-tier", "spell") worked with the exception of "guild-crest".