The cops would look at whether you're carrying a weapon dangerous to the public peace. That's a question of how they interpret your intent, based on the context and your behaviour. The test is reasonability: would a reasonable person consider that knife appropriate to whatever you were doing?

Note that self-defence is not considered a valid reason to carry a weapon except under very limited circumstances.

Carrying that knife downtown would result in it being confiscated, and probably in charges.

Carrying that knife while hunting or fishing probably wouldn't raise any eyebrows -- unless you got involved in an altercation.

scafool's test is the right one: would you question it, if you were a cop?