This may be the case for your city/locality, but statewide, there is no such requirement to conceal a folding knife. Statewide, there are relatively few restrictions on folding knives, no length limits, double edged OK, locking/non-locking OK. Autos are the only real restriction on folders statewide.
Big cities like Los Angeles/SF may have the backwards laws requiring concealment, but thankfully those are not statewide. Always check your local restrictions.