That's a good question...generally speaking, a clipped knife is usually considered open carry if any part of the knife is visible. Maryland law does not restrict carry of any type of folder except 'switchblades' and a few other types of knives (bowies, throwing stars etc.), which cannot be carried concealed. The restricted types of knives cannot be carried concealed "with the intent to harm someone". Now, this is where it gets into muddy waters...
The state has the burden of proving that you intended to harm someone, as they have the burden in proving any criminal charge brought against a party. Simple possession is generally not regarded as prima facae evidence of criminal intent (it's not NYC, where the opposite is true), but related actions and circumstances would certainly influence this. It would not take much for a simple possession scenario to turn into an arrest...the case may not stick, but you still will have to wade through the swamp that is the criminal legal system and will certainly lose your knife permanently.
As a general rule, I would suggest not carrying an auto in MD...the climate is very anti-weapons overall and a a number of municipalities have local laws more restrictive than state law (Balt City, OC, AA Co). MD knife laws overall are pretty loose (no restrictions on size, etc), bets to play it safe and stick to a manual or assisted folder if you want to carry it clipped (except in OC of course!).