Ticked Off! Those Pesky Pre-1850 Census Tic Marks

It's exciting when we are able to find our ancestors on every census they appeared on, until we reach 1840 and before. Those pesky tic marks seem to get in our way as we work to extend our pedigrees. Just what do they mean, and how can they help me? Are they throwing us into a dead end, or can they tell us more?