what is the "+" sigh in the modules folder name?

[Christopher Harvey]

I have a path on system called:
'/lib/modules/2.6.37+/'
It used to be called:
'/lib/modules/2.6.37/'

where did the plus come from?
I'm asking because I have a /lib directory and the kernel sources for 
it. the problem is there is a closed source driver in the /lib directory 
and I want to compile a new kernel image, but can't re-compile the 
closed source modules. I'm guessing my new kernel isn't working because 
it's looking in the path with the + after being recompiled.

thanks,
Chris