Unclear how they would convey the property title to you. If inherited, you get to use the stepped up basis to calculate the net income of the property when you sell which is a huge advantage. If they give it to you now, the basis would be the price they paid. If you buy it now, the basis would be your purchase price.
The 3.75% isn't the ROI, as you aren't including depreciation, maintenance, vacancy, nor capital appreciation.
edited to add a "what would I do" answer: Advise your parents to sell it. I think its a good time to sell in DC area. Invest proceeds in mutual funds. If they are eager to gift you money, or you need it, they can gift you each 14000 in 2013, and it is tax free to them. Consult a tax pro, but I think each parent could give a gift, each excluded from gift tax of up to 14K this year.