Multimodal graffiti are constrained by the environment in which they are written and by the activities in which graffiti writing takes place. This article examines graffiti collected in Graffiti Park and Nam Van Lake Underground in Macao. The graffiti in the two sites display systematic differences in topics, objectives, subjects, affordance, texture and framing, which are attributed to varied activity types and the multimodality/materiality of public space. Specifically, those in Graffiti Park – a small and secluded area – are products of one-off activities attended by professional writers, ordinary citizens and tourists. Nam Van Lakeside has a more visible space, and yet the graffiti there – largely murals painted by a few commissioned writers – display limited topics/themes under institutional appropriation. The materiality of the wall space also contributes to the variations in styles and contents of graffiti in the two sites.