In my tests, if you use assetic with the "?" character on filter, like this:
In my tests, if you use assetic with the "?" character on filter, like this:

{% stylesheets 'my/css/*.css' filter='?yui_css' output='css/packed.css' %}
<link href="{{ asset_url }}" type="text/css" rel="stylesheet" />
{% endstylesheets %}

And then use the assetic:dump command without --no-debug, even in prod environment, assetic will ignore the filter.
korobi/capifony,jeroendesloovere/capifony,pimolo/capifony,shipci/capifony,korobi/capifony,shipci/capifony,trsteel88/capifony,pedroresende/capifony,everzet/capifony,24HOURSMEDIA/capifony,pedroresende/capifony,jeroendesloovere/capifony,trsteel88/capifony,24HOURSMEDIA/capifony,pimolo/capifony,everzet/capifony