def update
    @profile = Profile.find(params[:id])
    @profile.form = "signup"
    ...
  end

undefined method `form=' for nil:NilClass

attr_accessible form
  ...
  validates :city_id, :presence => true, :if => :signup?


  def signup?
    #@profile.form == "signup"
    #@user.form == "signup"
    if self.form == "signup"
      return true
    else
      return false
    end
  end

def create
    profile = Profile.new
    profile.form = "signup"

    super
  end