Mention graffiti and most people get a mental picture of property that has been defaced, with walls, bridges and trains covered, illegally, by something often called "graffiti art." We think of it as existing on large public spaces and sometimes in small private spaces such as on the walls of bathroom stalls.

Actually, there's a whole lot more to it; in fact, it serves many purposes and has existed since ancient Egyptian times, long before cans of spray paint. Archeologists who study things like that note it provides an insight into a culture, not only what was chosen to be carved into the walls of the cave but also the degree of literacy of the "artist's" culture. It is a way of publicly affirming commitment, such as when someone carves a heart, around names, on a tree. When we engage in any of the many ways to display graffiti, we are passing on messages to the world about things that are important to us.

It's a way to mark territory or to record someone's presence at a particular location, such as Signature Rock on the Oregon Trail. Graffiti is a way of sending messages about one's social and political expectations. We all engage in graffiti of one kind or another to send those messages.

Just check out bumper stickers: this morning I saw one that said, "Don't take your organs to heaven. Heaven knows we need them down here." That is definitely a statement of someone's social expectations. And think about political yard signs and vanity plates on cars.

Another good example is Kilroy of World War II fame. The famous little character peeking over a fence, with the line "Kilroy was here," became a rallying symbol for the U.S. troops. One article about the origin and history of Kilroy stated that wherever our troops went, there would always be that familiar face to welcome them. Kilroy was always there before them, paving the way and then welcoming them. No one ever owned up to who drew those faces, and several stories exist about how Kilroy came into being. He is now permanently enshrined at the World War II Memorial on the National Mall in Washington, D.C., where he appears twice.

Take a look at posters that people choose to decorate the space around them when they have the freedom to do so. I once knew an employee who had two posters on the wall behind her desk. One said, "I know I'm somebody because God don't make no junk." The other was "Do you mind if I tell you to take your silly-assed problem down the hall?" Both are very negative messages, saying a lot about the person who chose to display them for everyone to see. Sadly, the person behaved in the same way, as if anyone who came to her for help - which was her job - had a stupid problem and/or had "put her down."

Over the years I have little by little built up a collection of t-shirts. None of us wear t-shirts displaying a message that we don't like or believe in. I remember one of mine that said, "A woman's place is in the house-and the Senate." Another was one I bought at the Guthrie, quoting that famous line from Shakespeare's "Henry the Fifth" about what to do with all the lawyers. Strangers often stopped me to say how much they liked and agreed with that shirt.

When I traveled alone a lot on business, I often saw ugly behavior between couples. One time walking through the San Francisco airport, I was behind this pair and the whole length of the concourse the man was berating the woman, whom I presumed to be his wife. Finally, I caught up with them and handed her one of the cards I carried for just such occurrences. I told her that the next time he opened his mouth to give it to him. It read, "You have just insulted a woman. This card has been chemically treated. In three days, your penis will fall off."

The woman stopped walking, read the card, and burst out laughing. The man turned around and very crabbily said, "What?" She handed it to him, he read it, let a couple of moments of heavy silence pass and then he too started laughing. She and I looked at each other, shrugged, and went on our own ways. When I looked back at them, they appeared to be getting along much better. Hopefully it stayed that way and he remembered that little bit of graffiti.

I am sure just about everyone hangs or puts graffiti on their walls at home. I do. My favorites around our house include one that has been on a bathroom counter for years: "A creative woman has cobwebs in her corners but not in her mind." Another says, "A friend is someone who knows all about you and still likes you." Still another, "Think purple when you are blue."

Some are more serious, like the one that says, "Courage doesn't always roar. Sometimes courage is the quiet voice at the end of the day saying 'I will try again tomorrow.'" My all time favorite is "A wonderful and wild woman lives in this house."

I suppose nowadays many people are posting their graffiti on Facebook. Mine is still on my walls. And, as in the case of that small card, in my wallet to be handed out as needed.