Do written warnings for driving offenses go on your record?

I got a written warning for "careless driving" becasue I did not realize the speed limit dropped it dropped from 50 to 30 apparently and I did not notice the sign becasue it was like 3AM and I was tired. I usually don't drive that late but I was pulling an all-nighter to finish some research papers for my college and I ran out of cigarettes and I had to get to the 24/7 tobacco store. I told the officer I didn't see the sign and I told him where I was going and I was polite and he sat in his car for a while so I figured he was printing a ticket. But he handed my a paper and said it was just a written warning. I have never been pulled over before so I was scared. So will this go on my record and what do I do with the written warning? Do I have to keep and file it? Will this look bad on my job applications? Will this effect my auto insurance at all?