Sigils are symbols of meaning and can be infused with intent, they are usually formed by using the shapes of letters is a word or in the positioning of the letters in a sentance.
Sigils can be created yourself easily and can be used in a huge number of situations from being stitched into clothing, to being used as paper in infused oils, you can even use them when making tea by writing them in sugar water on the bottom of your mug before you fill it with tea.
There are some amazing how to's online and many books can be found that include the creation of sigils as part of their contents.
Sadly I have never heard of servitor spells or their link to sigils, maybe someone else would have more to say on that topic.
I couldn't haw said it better myself. :) Use them well. Draw a symbol that is meaningful to you. It can be a bunch of squiggly lines or actually a picture of something. It doesn't matter as long as it has meaning. It takes on whatever meaning you give it.
Servitors are beings you can create in your mind, then release onto the astral plane if you choose to. They are non-sentient thoughtforms created to do any task you choose. They have no free will of their own.
Here's a link on servitor creation- http://johnkreiter.com/how-to-create-a-servitor-to-do-your-bidding/