I am new to Laravel and Entrust and this is one posible way:

in UserRepository.php class after "public function signup($input)"

    $this->save($user);
    //add
    $insertedId = $user->id;
    $user = User::find($insertedId);
    $default_role= Role::where('name', 'Default')->get()->first();
    $user->attachRole( $default_role);

I bet there is better solution for this, but I didn't found it.

A better way could be assigning role with the help of events!

• Create 'events.php' file under 'app' folder

<?php
Event::listen('user.signup', function($user)
{
	$userRole = DB::table('roles')->where('name', '=', 'User')->pluck('id');
	$user->roles()->attach($userRole);
	return false;
});

• Include events.php file from start/global.php

require app_path().'/events.php';

• Fire the event on signup (From your user controller's sign up function)

Event::fire('user.signup', array($user));