According to Vinceti, they appear to be the letters ce or simply the letter B. Other symbols would be hidden in the landscape, more precisely in the arch of the bridge.

Volunteer: the Expo Center is located in the riverside green space of Zone B, to the east of Lupu Bridge.

For example, if 3 clients existed each putting to separate bridge queues, b1, b2, and b3, all remote queue definitions could have an alias of b.