What will be issued to establish meeting points on single track, except where rule 261 is in effect?

The correct answer is Form L, which is used specifically for the purpose of establishing meeting points on single track when rule 261 is not in effect. Form L is an official document issued by the railroad that outlines specific instructions regarding train movements, including the designated locations where trains are permitted to meet and pass each other safely. This is crucial on single-track lines where train operations must be carefully coordinated to ensure safety and efficiency.

Form L provides clear and detailed instructions that are communicated to train crews, ensuring they understand the established meeting points and any associated operational requirements. This form is particularly important in situations where trains are operating in both directions on a single line, ensuring that each train knows where to expect another and can manage its movements accordingly.

In contrast, the other answer choices do not specifically serve this purpose. An operating manual contains broader operational guidelines but would not provide the specific information needed for meeting points. Signal flag instructions, while important for communication and signaling purposes, do not address the operational details for meeting trains. Meeting point guidelines might seem relevant, but they are not the official documentation used in the context of railroad operations; that responsibility falls to Form L.