A lot of Amāq statements on IS inspired attacks, like the one in Charleroi, quote : مصدر أمني
Yet the correct translation would be ‘a trusted (or reliable) source’ as the Arabic verb أمن in Classical Arabic means ‘to be faithful, reliable, trustworthy’ (The Hans Wehr Dictionary of Modern Written Arabic, p. 35)
Mostly, in my impression, these ‘reliable sources’ refer to official statements as reported by Western news agencies or, in some cases, exclusive reports by these exact same agencies. Then, once noticed by the network behind the Amāq news agency, attacks like the one in Charleroi might be chosen to enrich the propaganda. Once out, the idea or hint that it indeed was IS related gains the upper hand. And hence, IS scores twice, it can not only claim the attack but also ensured enough media attention to keep us busy until the next hit.