Assuming this is below the surface of the glass and not simply a spill: looks like a seperation between the outer glass and the substrate. They are simply glued together so it's possible that with enough age and heat that they are simply coming apart.
What to do if you find yourself stuck with no hope of rescue:
Consider yourself lucky that life has been good to you so far. Alternatively, if life hasn't been good to you so far, which given your present circumstances seems to be more likely, consider yourself lucky that it won't be troubling you much longer...
-- Excerpt from the Hitchhiker's Guide to the Galaxy.