I created a crosshair texture in Photoshop:
In the material I add this code:
In game:
If you wish to scale the material use the ScaleUVsByCenter Material Function:
Result:
To fix the stretching, Add a TexCoord and modify the U / R channel, then offset it using an add:
Result
Edit: There is a smart solution you could use where you get the viewsize and do some trickery with the UVs. I am way to tired to finish this and make it look good, but that way you can retain the proper texture size and have it centered. I have a 1920x1080 monitor, so you might want to change the add -0.45 to something else.
