The one youre describing is probly the one i think of as the Fireball Marker. Large-ish orange triangle(point down) with like a big glowing dot in the middle? For comparison, the one OP is talking about(and the most common one in general) is this - the design of which at least to me screams everyone get here(note: not everyone typically has to stack for these, but the more people in the marker the easier it is for the healers to handle so certainly better to share if youre in reach - and certainly dumb to run away from everyone if youre the one with the marker on you).
And i think in general the reason we have so many different indicators for this is that some of them are slightly different. Stand with 1+ other marked person to avoid bad effect isnt technically the same as everyone stand together to share damage. But functionally? Theyre certainly similar.
Edit: I dont own that image, i just snagged one of the first ones to appear on a google image search for ff14 stack marker.