I got a ticket for this after parking in a metered bay in Bold St, the ticket guy said this rule has been in force for 3 years now and there are marked motorcycle bays across Liverpool, although he was not able to offer me any information on where to locate them!!
I tried to appeal saying there were no notifications of the change, apparently the notification is on the meter, i argued that since parking for free never required me to visit the meter how was I supposed to notice the change in rules?
I eneded up paying £150 in total.
Problem is, if you decide to appeal, you have to wait until the payment deadline, and they know they can get at least £70 out of you if you lose.
I paid the £35 just before the deadline but I haven't actually gone back to look at the noticess on the meters, as I took their word for it.
I had parked my bike in Hawke Street which is off Copperas Hill, and haven't been to Liverpool city centre since.
Next time I go over there I will take some pictures of parking meters and if there is no reference to motorcycles, I will complain to the penalty tribunal:http://www.trafficpenaltytribunal.gov.uk/site/scripts/documents_info.php?documentID=70