The little nubbins sticking out of the head of Demetrius Poliorcetes (if that’s the correct identification of these statues) are the base of goat horns that have broken off. These aren’t on a helmet, but are still clearly part of the royal iconography of Philip V’s predecessors on the throne of Macedonia. (Images and Discussion from Pollitt; Cf. also Ridgeway 1990: 125).
My concern over the identifications is based on the oft-stated ‘similarity’ between portraits in the round and coin iconography for Demetrius. On the coins he wears bull horns from the his temples not goat horns from his hairline right over his forehead:
Coins link to Acsearch.info. I chose these two types both for the portrait variations they represent, but also as nice comparative examples of early Hellenistic horse and rider iconography and a nice clear aplustre as a naval victory symbol.