At BDSM gatherings, events and parties a simple Left/right code is sometimes used. Anything worn on the left (like a whip, your set of keys or a set of handcuffs) indicates "dominant." But if these objects are hanging from the right side of your belt you are signaling "I am submissive, please use these things on me." So if you're visiting a party, you may want to be aware of where you hang your keys!
Another, somewhat outdated party code is the stud code. If your wristband or collar has pointed studs, you signal you are a dominant. Flat studs indicate submissive. However, if you are visiting a party do not count on it. In fact, at some parties no dominant would ever wear a collar, regardless of the kind of studs on it.
A small teddy bear on a leather jacket may (but, again, does not have to) indicate that the person wearing it is a "bear" - a daddy-type...perhaps looking for a little boy or little girl type to play with.
While the erotic power exchange does not have a common symbol, people will sometimes try to indicate their preference with small keyring size handcuffs or similar jewelry. However, since some people carry these just for fun (including police officers), this sometimes can lead to very confusing situations.
There are various other symbols around - none of them however is universal. There is the triskellion symbol for example (diffierent people have different meanings for it by the way) and in Europe people have tried to make a black square - like the gay purple triangle - the unversal BDSM symbol. These days most symbolism seems to be around in the Internet. Hardly anything can be found in real life situations.
Often what things mean will vary from one coast of the United States to another, so the international differences may be even more pronounced.
These codes are simply examples of what some use to signal others about their interests. As a general rule of thumb, NEVER take anything that even remotely looks like it could be a code for granted. Ask! You may run into all sorts of awkward situations if you don't.
