Yes, it is an admission of guilt. Plain and simple. And by signing the ticket, you have given the officer the ability to hold "roadside court" in which he is the judge, jury and executioner and can dole out punishment, including but not limited to summary execution. He will dispatch you with his issued duty sidearm.
Now, this is hardly used today, but dates back to mid 1800's or so, possibly farther back, where the marshall could try and convict you of stealing horses and then execute you by hanging while the crime was fresh and courts were few.
This is why you should try and escape the offending officer always. Your best defense in court would be that you were in fear of your life - if you make it to court. It's best to make the officer "work for it" than just rolling over and showing your belly.
Fight it with all your might. Your very life could depend on it.
BTW, I always sign them and have never been executed yet. But one day I might be.