Which sign indicates that a parking area is available?

Answer: A — Blue sign with a white 'P'

The blue sign with a white 'P' is a widely recognized symbol indicating the availability of a parking area. This specific sign is used in many regions and communicates to drivers that they can park their vehicles in that designated area. The clarity and color choice—a blue background with a contrasting white 'P'—make it easily identifiable for motorists, ensuring they can quickly locate parking spaces when needed. In contrast, the other choices do not convey the indication of parking availability. The red sign with a white line typically denotes restrictions or no entry; it suggests that parking is not allowed in that area. The green sign with a bicycle symbol indicates facilities for cyclists, not parking for motor vehicles. The yellow sign with an arrow could point to various directions or instructions but does not specifically relate to parking availability. Thus, the blue sign with a white 'P' is the correct choice for denoting an available parking area.