I haven't found the ability to modify your crosshair in Unvanquished. In Tremulous, I used dot xhairs by using a modified HUD (which I further modified because the default was a microscopic red dot), but in my opinion a larger selection of crosshair styles should be available from the start, as most contemporary games will allow you to do. I'm personally enjoying dot crosshairs a lot, but people's preferences can differ.. At any rate, I was wondering if there was some particular reason for not putting the option in, and if not, would like to suggest giving the option to players :)
Some more common designs: