Look up local laws. They are all different. Maybe check out KnifeRights.
Edit to add:. I know what is legal in my local, but I've also been carrying a knife as far back as my memory goes. As such, I don't really consider it a weapon, therefore have little desire to blurt out "I've got a knife!". Now the forty five on my belt, that's a different story.
Early on in my carry, it was law to inform Leo's of your firearm. Later the data was merged with vehicle/license data, and now screen pop's, so the law changed to not require verbal notice. Since that time I got pulled over in a freeway speed trap. At the end the officer asked if I was carrying, I said yes. He then asked why I didn't notify him earlier?. I stated simply that it was not required, and I knew that he already knew also. He just smiled said thank you for taking measures to protect your own family.
Then a few months ago I got pulled over again by a local. I decided to give verbal notice as a courtesy. He asked where it was, replied "hip", he said "fine", and went on his way writing my ticket.
So, meaning to the stories, cops deal with a ton. Unless you look suspect, act suspect, or are suspect, I doubt anyone would give a second thought to a knife....unless it really is illegal where you are or what you carry.