Vacant is a tiny poem about emptiness that turns emptiness into something. The speaker begins with "nothing to signify nothing," which sounds like a shrug: there is no meaning here, and nothing to say it with. But the next line flips this around. Out of that blank, the speaker "makes a meme." The word is a clever choice. A meme is a small, quickly passed-around unit of an idea, and here it suggests that even a void can produce a little spark of expression.
The last two lines shift the tone. "Simple yet right / like an evening in the country" calms everything down. The speaker seems to feel a quiet satisfaction, as though the result, however slight, fits perfectly. The mood is light, wry and peaceful. Rather than being troubled by having nothing to say, the speaker finds a gentle contentment in it, the way a still country evening needs no extra decoration.