Emojis are ubiquitous in digital communication, and brands widely integrate them into social media marketing. Drawing on research on cognitive busyness, multitasking, and the Affect Infusion Model, we propose that emojis function as context-dependent affective cues rather than uniformly processed signals. Across two studies, we examine how cognitive busyness shapes their impact on brand evaluations. Study 1 shows that under cognitive busyness, emojis serve as salient affective shortcuts, increasing reliance on heuristic processing and leading people to use emoji-elicited emotions as proxies for brand attitudes. Study 2 further demonstrates that emojis enhance ad liking, but this effect is contingent on perceived selling intent. When cognitively busy, people rely on immediate affective responses, increasing positive evaluations; when not busy, they engage in more deliberate processing, interpret emojis as persuasive cues, and attenuate affect infusion. These findings highlight the boundary conditions and underlying mechanisms of emoji effectiveness in social media marketing.