"It's not that I have ideological differences, I'm just not a hat person"--S. Griffin
Yarmulkes kinda fascinate me. It's not just the fact that there's a random r in there. It's the whole set of assumptions and practices associated with them. The amount of thought and calculation on behalf of boys that goes into wearing them is so interesting. For example, I was talking with a friend at a bar-birthday-party one Saturday night. He'd gone to shul a couple hours before and had decided to leave his yarmulke on even though he doesn't normally wear it outside of services. He said he was contemplating wearing it full-time. Why, I asked. He said he realized that a lot of girls weren't even looking at him as a datable option because of his lack of the yarmulke. That they assume that he's not observant because of this one thing. (He's pretty kosher and semi-Shomer Shabbat.)
Even though it may sound like a silly reason to start wearing one, he's sorta right. There is a whole set of assumptions that goes along with this outward signifier. A lot of times you hear the latest gossip about some guy, and even though you don't know him that well, the surprised response is "But....but.....he wears a yarmulke!"
Then there're the guys who do the reverse. They take OFF their yarmulkes when they go out to clubs. Sorta like G-d can't see what they're doing unless they wear their homing device.
I guess it all comes down to trying to get the ladies.
Speaking of the ladies, we use physical objects to signify identity, too. I was talking with a few girls the other day at Starbucks. One of them was saying how she feels more religious when wearing a long skirt, like she has to pair it with a long-sleeve T-shirt. We were also saying how it almost makes us feel like imposters. That by wearing a long skirt we're somehow telling people we're something we're not. Like so much meaning is wrapped up in your day wear. I have to admit, I did get really excited when I saw a group of yarmulke-clad tourists walking down the streets of Prague after going so long without seeing them last spring. I could assume they were craving non-existent Czech kosher meat just like I was. :)
Of course, girls can also adopt a Jewish identity by wearing a yarmulke themselves. I saw a woman walking down University wearing one a couple days ago; the first time I saw a woman wearing one outside of shul, I think. It's really interesting how girl-yarmulkes tend to be crocheted or pink or purple. Like they're taking this masculine object and imbuing it with their own feminine identity.