Symbolism, Imagery, Allegory
Jacob wanted to put a ring on it, but Geertrui said no—he was already married to Sarah after all. But the couple still wanted to exchange tokens of their love for each other, to make their love more official, so to speak, so the tokens operate almost like wedding rings. That they are not wedding rings, of course, reminds us that Jacob is already married to Sarah, who waits for him back home.
We know that the geveltekens—or facade-signs—have "a broom to brush away thunder, a tree of life, a sun-wheel, and a chalice or cup" (19.44) on them. Doesn't that just scream romance? Okay, maybe not. But have no fear—Geertrui is more than happy to break down the significance of these images. She explains in her memoir that when they exchanged their tokens, Jacob told her that the signs are to:
[…] ward off the thunderous wrath to come for loving me, feed you from the glorious tree of life, ever cause the golden sun to shine upon you, and always fill you to the brim with pleasure in being my beloved Geertrui. (19.44)
Pretty romantic after all, isn't it? The symbols represent different aspects of love—protection, happiness, pleasure, and the like—and that they consistently reference the future shows us that Geertrui and Jacob are not just some fling, but care a whole heckofa lot about each other.
Geertrui tells Jacob that the symbol is more special to her than any words because it represents Jacob's love for her—it's not about the actual token, but more about the feeling of love and affection she gets when she looks at it. It's just theirs.