If you are machine quilting, I use a Clover hera marker for marking lines . They use to sell them at JAF but I don't know if they still do. If your want to see what one looks like, then do a search on eBay. I am certain someone has a picture. Painter tape is also easy but remember you always want to reference from you center starting line to make sure you are still accurate with your spacing.
GOOD LUCK!!!