From the UK's CAP 413 - Chapt 2 para 1.8.2 - on aircraft callsigns "The name of either the aircraft manufacturer, or name of aircraft model, or name of the aircraft category (e.g. helicopter or gyrocopter) may be used as a prefix to the callsign.".
A couple of paras later it says "Aircraft in the heavy wake vortex category shall include the word ‘HEAVY’ immediately after the aircraft callsign in the initial call to each ATSU."
It's worth pointing out that the UK uses non-ICAO wake vortex categories too but offhand I can't remember whether heavies are different.