Comply according to ADA Accessibility Guidelines, section 4.6.4., "Accessible parking spaces shall be designated as reserved by a sign showing the symbol of accessibility". Provide clear, required marking for your handicapped parking areas.
Disabled Parking Signs. A parking space on private or public property, Including schools, businesses, libraries, hospitals and government buildings that is reserved for persons who are disabled shall be marked by a sign affixed to a post or a building. Sign shall be clearly visible to anyone directly approaching that particular space. Clearly marked handicap parking spaces and entrances will help your customers and employees with disabilities easily access your building. Handicap parking with symbol signs also remind other patrons to respect your parking rules. Handicapped parking spaces must be marked with a sign featuring the international symbol for accessibility. The sign must be tall enough that it can be seen even when the space is in use.