I believe
That there is a phone number on the ticket that you must call before ~21 days to the justice of the peace.
When you make this call and talk to the JP don't be on the defensive to much, something along the lines of, "I can't believe I didn't see that sign." should work. You should tell the judge that you do not want to contest the ticket (nolo contende) and inquire if there is a way to keep this off your driving record.
The judge has a minimum and maximum fine that he/she can hand out, plus can order you to take a class within a certain time frame that reduces the fine. I would expect a driver's safety class and the minimum fine would be handed out. Everything from there is then handled by mail. You can take a comedy driver's class for (guessing here)$30-$50 bucks and probably face a fine of (still guessing)$75-$150.
I have a friend who is a JP here who says that she feels no remorse when she gets a phone call and the person feels that there has been some kind of great injustice done and how he/she was singled out of 6 billion people to be the unluckiest person on earth. She says, "I guess I'll see you in court then." to those people.
Instead she'd rather hear a valid excuse for the infraction, 'i didn't see the sign.' Hear atonement, 'I'll never make this mistake again.' And willingness to do something to prove that your serious, 'take a driver's safety class.'
I hope it all works out for you.