She had a meeting with Bobby and some clients of the show and decided to wear a new shirt. With a new shirt comes tags and she had forgotten to take the tag off of it. It was sticking out of her shirt in the back, but it wasn't until after the meeting and she was leaving twork that Scuba Steve alerted her of the tag sticking out. Amy was super embarrassed that no one said anything to her before that moment, especially because she had interacted with clients like that.
Bobby admitted that he saw it when they walked into the client meeting but just thought it was possibly something that went with the shirt.