Which of the following restrictions apply when appending a self-assigned call sign indicator?

The correct choice reflects the requirement that any self-assigned call sign indicator must not conflict with existing call signs specified by the FCC rules or with call sign prefixes assigned to other countries. This means that when a ham radio operator selects a self-assigned call sign, they need to ensure that it is unique and does not duplicate or interfere with those already in use. This rule exists to prevent confusion among operators and to maintain a clear and distinguishable communication system.

When selecting a self-assigned call sign, it’s crucial to check that the chosen indicator does not match established international standards or fall into a range utilized by other operators. The goal is to ensure all operators can communicate effectively without any ambiguity regarding who they are addressing or who is responding to their transmissions. This helps maintain order and clarity in the airwaves, which is essential for effective amateur radio operation.