parking on a grass verge

[gjc66]

I was park on a grass verge out side a friends house waiting for my son. I was sat in the car and the engining was running. there were no sign up to say I could not park there but I got a parking ticket. when I asked why I was getting a ticket the warden said I was not allowed to park there. I commented that there was no signs to say I could not, and he said that there were no sign to say I could and walked away. was I in the wrong if so why.