How to abstract enum attribute used by multiple models in Rails?

I have a database attribute called currency which is used by multiple models. I'd like to create a concern (or similar) which defines the basic functionality of the currency attribute. If it was only used in a single model, I'd probably do something like this:

class Transaction < ApplicationRecord
  enum currency: [ :USD, :AUD ] 
  validates :currency, inclusion: { in: currencies.keys }
end

But since it's used by multiple models, I'd like to do something like this instead:

class Transaction < ApplicationRecord
  include Currency # maybe in a Concern?
  acts_as_currency :currency
end

The whole idea is to be able to do things like Transaction.first.currency.USD? and similar functionality that an enum attribute has, as well as defining the attribute validation in a single place.

How would you design that with Rails? Is there any preferred way to do so?

In Ruby, shared behaviours call for modules, ActiveSupport concerns provide cool syntactic sugar, e.g. included

# app/models/concerns/has_currency.rb
module HasCurrency
  extend ActiveSupport::Concern
  included do
    enum currency: [ :USD, :AUD ] 
    validates :currency, inclusion: { in: currencies.keys }
  end
end

class Transaction < ApplicationRecord
  include HasCurrency
end

We can give the user of our concern more freedom by going through a function instead, as you seem to suggest:

# app/models/concerns/has_currency.rb
module HasCurrency
  def acts_as_currency(column = :currency)
    enum column => [ :USD, :AUD ] 
    validates column, inclusion: { in: column.to_s.pluralize.keys }
  end
end

class Transaction < ApplicationRecord
  extend HasCurrency # Note the `extend`, not `include`
  acts_as_currency
end