1.
Start Tremulous again at the main screen
2.
Click the tilde key (~) to open the console.
3.
When the console opens (The black box that comes down when you press ~), you can type messages in it. Now type in:
cg_drawcrosshair 1
Exactly as shown above, it doesn't matter if you use caps or not.
If that doesn't work, also try:
/cg_draw2d 1
4.
Go to a server and try it. If your problem isn't fixed, reply back here. Hope this helps, cheers.