I don't really understand what you are trying to say. Negative as well as positive pressure is possible in solid materials under stress, when you consider the classical stress tensor: http://en.wikipedia.org/wiki/Stress_(physics)

It is sufficient to pull on a solid to instore a positive normal stress (= negative pressure)...

Probably the most useful comment from the above link is the following. Note that the cosmological constant is one specific form dark energy could take.

I am assuming you are referring to stresses. In that case it's analagous to acceleration in that the minus sign simply indicates a direction or trend. And in that you are correct. I guess it's in how I was taught. I didn't realize that cosmology (as Pervect pointed out) utilized the negative pressure idea.