How on earth can they enforce this?
Voluntary compliance from out of state vendors and package delivery services such as UPS, FedEx, etc. seems unlikely, as doing so would hurt their business in sales and require extra time and expense to enforce. Unless the return address or something else on the package identifies the contents as cigars there isn't anything to indicate what's in the package, so one would assume cigars could and would be delivered to Maryland addresses sliding under the new law ... hell, if Cubans cigars are getting to customers from Switzerland tax-free in spite of Federal and State prohibitions now, I don't see how Maryland can do any better enforcing theirs.
Many states, in violation of the Constitution, have attempted and are still trying to regulate interstate commerce, which is what Maryland is doing in this case. Interstate commerce is under the sole purview of the Federal Government. Thus far, most states have dropped this nonsense and satisfied themselves with the status quo (i.e., you pay taxes on your taxable items if the vendor has a B&M in your state -- otherwise the customer who owes taxes on goods purchased out of state -- via the internet, on the phone, by USPS, UPS & all package delivery companies, or in person -- is personally and legally required to report and pay for any and all state taxes due on their purchases).
Slightly off topic, but of serious concern and an on fire topic on the foodie, wine, liquor and beer blogs is a current push, instigated by highly paid Congressional Lobbyists representing beer, liquor and wine distributors nationwide, to urge the passing of a Federal Law (HR 1161) banning all interstate shipments of wine, beer and liquor. This is immensely popular among the members of Congress (already dozens of co-sponsors) because these distributors contribute large sums of money to both parties and to politicians' campaign coffers. Read more about this and what you can do about it here:
http://www.zesterdaily.com/zester-soapbox-articles/903-wine-shipping-politics-hr-1161