Barrier systems with interlocking flag

A barrier assembly comprising:

• a barrier having an interior surface bounding a chamber and an opposing exterior surface, the chamber being adapted to hold a ballast, an inlet being formed on the barrier so as to communicate with the chamber;
• and
• a flag assembly comprising:
• a post having a first end and an opposing second end;
• a flag disposed on the first end of the post;
• and
• a retainer disposed on the post and comprising a catch radially outwardly projecting from the post, the catch being movable between an outwardly extended position and an inwardly retracted position, the catch resiliently urging toward the extended position when in the retracted position, the first end of the post being received within the inlet on the barrier so that the catch is disposed within the chamber in the extended position, the catch being configured so that the first end of the post cannot be pulled out through the inlet without moving the catch to the retracted position.