What is the appearance of expired brown sugar?
Any package date would be a "best by" date, which would indicate quality, rather than safety. Really, the only risk is that the flavor has degraded.  If the sugar is hard, you can put it in a microwave-safe bowl with a damp paper towel.  Cover the bowl and microwave in short bursts (10 - 15 seconds), breaking up the hard lumps with a fork in between bursts.  Be careful not to melt the sugar. Then use as you wish.