As you can see, there are three circles. The top is for poly or monogamous. The right circle is straight, bisexual, gay, or lesbian, and the bottom circle is available, involved-available, or involved-not available. The circles are color coded so that people who are familiar with the buttons can read them with a quick glance.
What are they for? They are excellent for any situation in which it would benefit you for people not to need to guess your dating status such as a club or a party. The first step to being able to meet someone is that they know that you are available. Perhaps that cute guy or girl over there is interested but assumes that you must be with someone else already. If only you had a button, they know know it was not true.
As always, you can find an image of the button appropriate to you to post on your LJ or other website on the site.
My Dating Status Button says:|
Polyamorous, Straight, Involved/Available
|Polyamorous||Interested in multiple serious relationships.|
|Straight||Interested only in the opposite gender.|
|Involved/Available||Currently in a relationship, and potentially interested in more.|