If you get pulled, you'll probably get a ticket (depending on your local PD) for failing to register. If you carry the bill of sale with you, you should be okay about the title. The DMV shouldn't care about how long you've waited to register it. And in NC, not sure about MD, a registration violation is a misdemeanor, but it's a fix-it ticket, so not a huge deal. Just carry all of your documentation with you and you should be good...assuming you have a license for a motorcycle as well, if not, that's a different set of problems.