Final answer:
A sign with a bicycle and a red NO circle indicates that bicyclists are not allowed to use that road. It's a prohibition sign meant for ensuring safety and smooth traffic flow.
Step-by-step explanation:
A sign with a bicycle on it and a big red NO circle around it generally signifies that bicyclists must not use this road. This type of sign is used to indicate restrictions and prohibitions for road users. In this case, it means that bicycles are not permitted on that route. It is important for the safety of bicyclists and the smooth flow of vehicular traffic that such signs are heeded.
The sign does not mean that only bicyclists are allowed, that vehicles cannot pass bicyclists, or that it is a no-passing zone specifically for bicyclists. Instead, it straightforwardly indicates a prohibition against bicycles on that particular road or area.