What is a common characteristic of vessels that are required to have proper lighting and shapes while at anchor?

Vessels that are required to display proper lighting and shapes while at anchor must adhere to this rule regardless of their size or type. The navigation rules specify that all anchored vessels, including both commercial and recreational types, need to exhibit these measures for safety and visibility purposes. The primary intention behind these regulations is to ensure that other vessels can easily recognize the presence and position of an anchored vessel to prevent collisions and ensure safe navigation in the area. Therefore, the characteristic that all vessels must comply with lighting and shape requirements while at anchor applies broadly, making the size or type of the vessel irrelevant to the necessity of following these rules.