Any parking spots marked in blue are supposed to be restricted to people who have the disc to put on the dashboard. Luckily, our hostess last year was able to obtain one for us, and we left it with her for the next renters of the studio. I know some have said they have parked without it, but there was a post last year of someone who got a ticket, and then had difficulty finding the place to pay.
We have also parked at the round about, on the dirt area. It's free. We have also parked on the other side of the marina, near the Cafe de Paris side. It's also free, but sometimes there's a man to try to get you to pay for parking or a car wash.