Derk, do you really want to jinx yourself by asking this question?
The two most noticeable symptoms would be falling oil pressure and knocking sound(deep for main bearing, a bit less deep for rods) that gets louder and louder.....Both are due to the increaded clearance between crank and bearing.
If you ignore the symptoms, there will likely be a "BANG" sound followed by a dead motor and the ability on your part to closely examine internal engine components WITHOUT any disassembly required.
Keep your eye on the O.P. gauge. If it is showing pressure different than what you are accustomed to seeing, be wary. If you start hearing a regulary spaced knock, shut it off. Your headers may cover up some of the sound, but the difference will be apparent.