Apologize for a misunderstanding

Security guard: Excuse me. Can I have a word with you?
Dean: Yes. Is there a problem?
Security guard: I'm afraid so. Did you know that this is a private property?
Dean: No, I didn't.
Security guard: Didn't you see the sign?
Dean: No, I'm afraid not.
Security guard: Have you been here before to skateboard?
Dean: No, I live out of town.
Security guard: Well, if I were you, I'd look for a different place.
Dean: OK. Sorry about that. I didn't realize.
Security guard: That's OK. Remember for next time.