In my CCW permit class, the instructor advised use that we could open carry anything (not firearms).......even a katana, as long as it open carry and not concealed. He said when it comes to concealed knives, that it is up to officer and judge discretion. Some may feel a 4" knife is fine, while others may feel 3" is the limit. He advised us to either open carry, or to carry concealed with a CCW permit.
In practice you'll probably be fine with pretty much anything. The only times I have head of people being convicted of carrying knives, was when they were doing something else illegal and that got tacked on as an additional charge.
However, they didn't let me take my 1.5 inch Vic Signature into a courtroom. I thought that was a bit silly, but I guess that's where we are post 911.