We list Mrs. Bell as a symbol and not a character because we don’t really know anything about her. And we don’t need to. She serves her purpose just fine by 1) giving the reader more information about Andreson, and 2) having a name that isn’t Mrs. Hirsch.
It’s this second one we want to talk about here. We’ve already talked about how appearances are deceiving in "The Killers," so at first it looks like this is simply another example. Nick thinks the landlady is Mrs. Hirsch, since the place is called Hirsch’s boarding house, and she ends up being Mrs. Bell. OK. Confusion, uncertainty – same old same old.
But Hemingway drops a hint that there’s more going on. Check it out in context:
"Well, good night, Mrs. Hirsch," Nick said.
"I’m not Mrs. Hirsch," the woman said. "She owns the place. I just look after it for her. I’m Mrs. Bell."
"Well, good night, Mrs. Bell," Nick said.
"Good night," the woman said.
Nick walked up the dark street to the corner under the arc-light, and then along the car-tracks to Henry’s eating-house. George was inside, back of the counter.
In case we forgot that the lunchroom was called "Henry’s," we get a little reminder. Mrs. Bell is running Hirsch’s boarding-house, and George is running Henry’s lunch-counter. On top of that, the killers haven’t met Ole, they just want to kill him. Everyone’s a hired hand. Everyone is acting on behalf of someone else. In a way, this Bell/Hirsch, George/Henry stuff gets the killers off the hook, as far as the reader’s judgment is concerned. It reminds us that they’re not calling the shots here; they’re just doing their job. And that, too, makes it easier for us to smile a bit at their antics instead of disliking them for being murderers.