Yup, just ask permission. If you have no radio, you need to have a vehicle with appropriate lights(flashing yellow, or whatev they say).
As for the fine, it's muni and he might be right. The rules at public airports are onerous. If you want to read some real BS crap, pull up the rules for operating at Cleburne.
<edit: Yup, found it:
Sec. 3-102. - Vehicle and pedestrian communications in airport movement areas.
(a) Taxiing aircraft shall have the right-of-way in preference over pedestrians and all other motor vehicles at all airports.
(b) At any airport that has a control tower, it shall be unlawful for any person to walk or drive a vehicle on or across any portion of a movement area unless (i) that person has received proper authorization from the control tower to walk or drive on or across any portion of the movement area and is in and maintains constant radio contact with the control tower while walking or driving on or across any portion of the movement area or (ii) for an operator of an aircraft or other motor vehicle, that person has received a light signal or similar clear permission from the control tower prior to operating such aircraft or other motor vehicle on any portion of the movement area.
(c) At any airport that does not have a control tower, it shall be unlawful for any person to walk or drive a vehicle on or across any portion of the movement area unless that person has received proper authorization from the director or authorized designee to walk or drive on or across any portion of the movement area and (i) is in and maintains constant contact with the authorized UNICOM operator by way of two-way radio or (ii) is under escort by an individual who is in and maintains constant contact with the authorized UNICOM operator by way of two-way radio.
(d) A violation of this section 3-102 shall constitute a misdemeanor criminal offense punishable by a fine not to exceed five hundred dollars ($500.00). >