HHI Fire/Rescue uses a different method than traditional Tone-out for station alerting. I don't know exactly what system they use, but it's a digital system that does not use voice. If you tune to 453.075, you'll hear the data being transmitted from time to time. I have heard a more traditional tone-out and voice on this frequency for Daufuski Island, but only as a test. I believe they test on Monday evenings, but I'm not positive about that. I don't spend a lot of time there, and mostly on weekends. I have only caught that tone-out test once.
The dispatcher will announce calls via voice on the primary dispatch talkgroup (550) on Palmetto 800. This is only heard on the Beaufort County simulcast site (Site 1-63). I believe this announcement is typically preceded by a tone, but it's just a generic alert tone, not something unique to each station or unit being dispatched.
Hope that helps.
Brian