The first squirrel to show an interest in us had a big round notch in his right ear, as if someone had taken a hole-punch to it. I dubbed "him" "Notch". Later we found out that Notch is a "her".
Notch at first was fairly aggressive and definitely considerd our backyard (and several neighboring yards) to be her territory. She can sometimes be seen up on the power lines barking at invisible enemies who dare to intrude. But as time passed she became more tolerant of other squirrels.
She's still the ruler of this yard, though. If she's in a mood to eat, no other squirrel had better get in her way. And she holds her own against cats, too: she scolds them from a perch in a tree or on a wire, and Dave saw her holding a staring matche with one when she saw it while crossing the street. She knew she could get up a tree faster than the cat could follow, and the cat knew it too. I hope she's as smart about staying away from cars.
In winter, she has bright white chest fur which she flashes as she sits surveying her domain. Her summer coat has a lot more brown and red, and her summer belly is brown spotted with black and tawny.
Notch is pretty friendly: she'll come to the door, scratch to make sure we know she's there, and take nuts from our hands. She's very picky about what she takes, though: she likes walnuts in the shell, and hazelnuts are okay if she's in a burying mood. If she's hungry she'll sometimes take shelled walnuts, hazelnuts or almonds. In guava season she eats a pineapple guava now and then. She won't touch peanuts (just as well, since they're apparently bad for squirrels), cashews, slivered almonds, pumpkin seeds, birdseed or corn. If you try to give her something she doesn't want (even a piece of walnut, if she's in a mood for something else) she'll either sniff disdainfully at it then look you in the eye expectantly -- "Now give me something real!" -- or pick it up and drop it on the ground.
We enjoyed Notch's company for about three years, but alas, about a week into caring for a litter of youngsters she disappeared. Motherhood seems to be a very dangerous time for wild squirrels, even supremely competent ones like Notch. We miss her greatly.