I received a ticket with "WARNING" written across the front. DO I need to pay a fine?

No.  When "WARNING" is written across the ticket, the officer is informing you that you have parked in a manner that is a violation of an ordinance or law, indicated by the box(es) checked on the ticket.  This is just as it says, a warning that you have done something that is a violation, but there is no fine associated with the ticket.  If you continue to park in the manner for which the warning was issued, you may be issued a ticket with a fine in the future.  Warnings are issued at the officer's discretion, or in special situations at the direction of the Chief of Police.