The phrase "sound one horn" is a common expression used to describe the action of signaling or announcing something. Some other synonyms for this expression could be to "blow one horn", "holler out", "call out", "announce loudly", "make a proclamation", or "declare loudly". All of these phrases convey the idea of drawing attention and making a public announcement. When used in the appropriate context, they can be very effective at getting people's attention and delivering a message. In summary, the use of different synonyms for "sound one horn" can bring variation to the language and enrich the value of expressions.