Lines drawn on with a white Sharpie.
I found that pencil markings disappear fairly quickly using a Simonis X-! for cleaning the cloth.
For snooker:
D radius is 1/3 the width of the playing surface
The D is at 1/5th the length of the playing surface
The Pink is 1/4 of the length of the table from the black rail
The Black is 1/11th of the length of the table from the black rail.
http://www.fgbradleys.com/et_spotting.asp
By comparison, the head string on a pool table is at 1/4 of the length of the playing surface.
On a 9 ft, the D would be at 20" and the pool head string would be at 25".