[Alamo-Girl]

I suspect the tagline is like a signature or logo, though I haven't seen it used exactly that way. I have seen it used on other forums (like DemocratsUnderground.com) to put a catchy quotation, condemnation or graphic to every remark a person makes.

[Condorman]

Taglines date back (at least) to the days of Usenet and dial-up message boards. Several message board packages (anyone remember BlueWave?) had built-in functionality to store and retrieve tagline lists, and randomly select one to append to every message.

For a short sampling of random taglines click here.