You're in their building, so I imagine your consent is stated as part of the ticket verbiage or in small print when you buy it. Regardless, closed-circuit cameras are pretty ubiquitous in private businesses, and have been for decades.
The idea of the poster was that customers are recorded during projection and that there is active real-time monitoring of said reception, e.g. to detect abuse.
So, "you are being watched as you watch". Not by an uncaring attendant, but by some actively processing automation.
