It incorporates the sun, from a blue sky with white clouds he painted - as his shop background. I remember reading that Spamton saw the sky of the Lightner world through the Shadow Crystal, that was inside the NEO body. And the triangles are colors of his NEO form. The two upward pointing triangles are the main colors of his wings, and the downward pointing triangle is the thing on the NEO body's chest. The downward triangle is pink and yellow like his glasses, and it also represents a Darkner in the Deltarune legend - like both Ralsei and Spamton is. And the Puppet Scarf is spread out like wings, that completes the symbol separately.

So this is an AU (Puppet Fighter?/Scarf Fighter? - maybe) if Spamton had the Puppet Scarf, and used it to fight with. Like this could be when Kris and the gang give it up for a different better weapon or armor from shops, boxes, or the other secret bosses. Or after the events of Deltarune end.

He'll wonder what to do with it, and then think about how Ralsei wields his scarf. Ralsei demonstrates and teaches Spamton how to use the Puppet Scarf on the practice dummy. And Spamton sees that, he can go way farther than Ralsei is willing to do, with his own methods.