(see SMW issue 2825).
{{#set:
Has URL={{SERVER}}/w/images/2/2e/SMWConFall2017Logo.png
}}
{{#show: {{FULLPAGENAME}}|?Has URL}}
The link below should be clickable as a relative url: https://www.semantic-mediawiki.org/w/images/2/2e/SMWConFall2017Logo.png
