OK, found this site:
http://pweb.netcom.com/~brlevine/md.txt
Which includes citations of various case laws, including:
- "'Gravity knife' constituted a dangerous or deadly weapon."
(1964)
- "Pocketknife with the blade already open did not require
any time to open the knife, as one would with a penknife,
contained all the offensive qualities of a switchblade or
gravity knife because it was instantly available for
violent use, and was not a penknife within the statutory
exception." (1990)
- "On the face of the statute, there is no indication
contradicting the view that a penknife is a penknife
whether small or large, whether the blade is closed or
open, whether the blade is locked open or unlocked, and
whether it is carried concealed or openly." (1991)
- "A folding knife without switchblade but with a locking
device... falls within the exception for 'penknives
without switchblade" in this section." (1986)
- " A buck [sic] knife (a knife having a blade which folds
into the handle and which locks into place when open)
carried with the blade open was 'penknife without
switchblade' within statutory exception, and this status
was not altered by knife's blade-locking device or fact
that it was carried with its blade open." (1991)
Notice that the courts disagree with each other with regard to carrying a folding knife in the open possition. Regardless of that, they all rule that a closed folding knife is legal.