Yes, there is a rule. Modifiers modify the closest (by location in the sentence) relevant word in the sentence. "In Service" could modify many things: "references", "guidelines", "supervision", "ships". However "ships" is right next to "in Service" so that would be the one it modifies unless there is a strong reason to believe otherwise.

"In service" is defining "ships." It means ships that are currently being used. The opposite would be "ships that are no longer in service" (they're no longer used) or "ships that are not currently in service" (they're not being used right now- perhaps they're being repaired.) "In service" isn't normally used with a noun like "guidelines." It's usually used with mechanical things that wear out over time like ships, boats, planes, cars, trucks, and major appliances. One slightly different use is with taxis. If a taxi is "in service", the driver either has passengers or is looking for passengers. The opposite is "off duty."

Thank you, Janothan. I think you have given me the most clear and excellent answer. I have got it and I do thank you a lot for helping me with a much confusing question.

Hi teacher, thank you for your answer. If I don't know the meaning of“in service”, how should I know the phrase in service modify guidelines or ships？