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Explanation
This is not a traditional comic but rather a personal message from Zach Weinersmith to his readers. In the image, Zach writes a note announcing that his book (likely "A City on Mars" or another Weinersmith non-fiction work) has been selected as Barnes & Noble's Pick of the Month for non-fiction, and that there will be a display featuring "the word Weinersmith" at Barnes & Noble stores.
The humor here is understated and meta. Rather than drawing a comic, Zach "interrupts" the comic strip to share personal good news, breaking the fourth wall entirely. He thanks readers for their continued support, noting that the book took about five years of research, and promises to "just get weirder from here on out." The tone is earnest and grateful rather than joke-driven, which is itself a kind of joke for regular SMBC readers who expect a punchline -- the punchline is that there is no punchline, just sincere gratitude. The sign-off includes a small heart drawing above Zach's signature, adding a personal touch.
This type of "interruption" comic is an occasional feature of SMBC, where Weinersmith uses the comic space for announcements, book promotions, or personal messages to his audience.