They were attached to any loco that was to travel through the tunnel, or associated with Channel Tunnel trains, ie diesel locos bringing trains to the UK portal at Dollands Moor to hand over to 92's. This is why the EPS 37/6's had the cast Polos as they were intended to bring the Nightstar Channel Tunnel Sleepers as far as the portal, the Railfreight Distribution 'European' 47's had smaller painted on ones under the drivers side window, as they were bringing freight to the portal. The EPS 73's just got them to look cool I reckon, used mainly for Eurostar towing and recovery