This is an old saying in politics and you're misinterpreting it - it's not about signaling to allies, it's about avoiding being held to any particular positions

This is an old saying in politics and you're misinterpreting it - it's not about signaling to allies, it's about avoiding being held to any particular positions. You're also missing the first half, "don't write if you can speak, don't speak if you can nod, and don't nod if you can wink." The point is not to commit to anything if you don't have to.