There are many different types of sign-up bonuses. Airlines give miles, hotels give points, and non-co-branded bank credit cards might givetheir own currency. Often, these programs are linked and miles/points are transferrable to each other. Even better, often programs offer bonuses for transferring miles or points!
If you are looking for travel, it is important to know what airlines you might be using as well as the partners you may be able to book with.