I have checked on the PA laws, and my impression as a layperson is that they are extremely vague. Other than switchblades, almost anything seems to go ... technically. I often carry a Pocket Hobbit, and don't worry about getting arrested if I don't use it in a threatening manner. However, the laws seem to give a great deal of leeway to police officers to decide if you are carrying your knife as a weapon. Also, they can easily confiscate it, even if they don't press charges of any sort.
-Fred