Humans are educable with a lot of patience and repetition. by Professor PeeWee, esquirrel
First, they have to voluntarily feed you. Show up, and bring a few friends so that they observe that you appreciate their efforts.
Put on a show Humans get bored easily and they like to see squirrels skirmishing for food dominance. Occasionally flick your tails at each other. Chase someone away to show who is the most deserving. Shove some nuts into your cheek pouches and occasionally run from the porch to the backyard as if you are going to bury the nuts.
Look cute. Make large, sad squirrels’ eyes at them. People call them puppy dog eyes, but show me a show the dog that can look needier than a squirrel on a mission to be fed.
Change your vantage point so you can keep track of when they might be available to feed you.
You can observe them from a nearby tree. If you see them approach the back door, immediately run down from the tree towards the porch. Reinforce that you are aware that they are your preferred take-out source. Await on the top of the stairs, the porch railing, or the back of one of the porch chairs. They become used to where you sit waiting for them. This is called positive reinforcement for humans.
When all else fails, get their attention. Like all large clumsy, animals, humans are not always the most astute things in the neighborhood. They can be preoccupied with almost anything flickering on a screen such as shadows on a blind, a television, or a computer. First see, if you can find where they are in the house. Sometimes there is a chair or tree limb near a window where you can peer into the house to see what they are doing. Other times, you want to throw yourself hard enough against the window to make a thud and get their attention. I know from experience, this works best with a window that has a screen your claws can grip when you thud against the window (otherwise you slip down the glass.)
PS Only pee on the glass as a last resort, humans have this unreasonable disgust of any natural animal process except feeding us.