Still, it should be more obvious than it is. Some kind of visual indication should be in place. The lack of such indicators on all types of NPCs as always been one of FFXI's biggest flaws.
You might be able to remember the locations of enough NPCs to get by, but chances are you haven't memorized the locations of every NPC in the entire game.
Why not? Every item in the game can each fit into a single inventory slot, regardless of size. Your haubergeon and stack of coeurl meat, for example, would each take up exactly the same amount of inventory space as a flower or a slip of paper would, not to mention how we adventurer's can carry around up to 240 items without any visible backpack of any kind. So clearly Vana'diel's items must be susceptible to some kind of inter-dimensional space/time compression, thus allowing any item to fit into almost any space. :P