I"m pretty new to playing, so have only done 1 boss so far (and found the place to summon the next), but both of them also had a visual clue, imo. Where you summon Eikthyr, one of the stones has an elk/deer on top of it, and where you summon the Elder there are sculptures of the ancient seeds on the top of all the stone pillars.
I'm assuming that trend will continue. Cryptic clue text PLUS a visual clue for each.