Final answer:
The question seems to require knowledge of specific maritime signaling procedures, yet without a defined standard or signal code provided, an exact number of rings to signal an obstacle to port is not determinable. Standard maritime signals are crucial for navigation and safety but vary according to specific protocols or international codes.
Step-by-step explanation:
The question appears to relate to maritime navigation and signaling, which falls under the broad category of social studies, specifically within the area of nautical knowledge. The specific situation described in the question relates to observing an obstacle from the bow of a ship, to the port side, and how to signal this information. In standard maritime communication, especially before the advent of modern communication devices, visual and auditory signals were essential for navigation and safety. However, the question does not provide a specific standard set of signals such as International Code of Signals or any maritime signal code that points to how many rings should be used to indicate an obstacle to port on the bow.
Without the context of a specific maritime signal code, providing an exact number of rings would be speculative. Signals may vary by ship, fleet, or even by country unless international standards are specified. In all cases, the safety of the vessel and efficient communication are the priorities, and alerts for obstacles would be clearly defined in a ship's signal manual or by the commanding officer's protocols.