How do I call a controller function from a template in Ember?

Let's say I have a template which iterates over a collection of items, and I want to call a function with each item which is specific to the controller, and not a model-level concern:

{{#each people as |person|}}
  icon name: {{findIconFor(person)}}
{{/each}}

I'd like to define findIconFor in the controller, because this is something specific to this particular view.

export default Ember.Controller.extend({
  findIconFor: function(person) {
    // figure out which icon to use
  }
);

But that doesn't work. The template fails to compile. Parse error: Expecting 'STRING', 'NUMBER', 'ID', 'DATA', got 'INVALID'

What is the "ember way" to do this?