Such a civilization wouldn't have much incentive to build 'keep off my lawn' signs, I don't think, given that the answer to such an advertisement should be a tr

Such a civilization wouldn't have much incentive to build 'keep off my lawn' signs, I don't think, given that the answer to such an advertisement should be a trillion relativistic snowflakes aimed at every system within a thousand lightyears. Anyone observing such a show of power would have no choice but to act first before that civilization did it to them.