This poster asks the audience (anyone who resides on Troost, Nearby Troost, Outside of troost, it doesn't matter) to write their name if they're interested in the annual Troost Festival.
Instructions at the bottom tell the viewer that once this circle is full of names overlapping etc. They will be scanned in and used for T-shirt designs making the Troost Fest T-shirts a collaborative effort while also giving a reason to go to the event (to see their shirt).
Also this is supposed to represent their visual identity tagline
"Every Person Matters"