Ever wonder: Is this a baby plant or a weed? Or, perhaps, is this a weed that is going to look pretty or ugly? (I personally don't mind the violets that pop up all over our lawn. They are purdy.)
Here's a site with lots of pictures if you already have an idea what you're dealing with: http://www.ipm.ucdavis.edu/PMG/weeds_multi.html and http://www.wssa.net/Weeds/ID/PhotoGallery.htm
Here's a site where you can search for weeds by their appearance: http://weedid.aces.uiuc.edu/
With all the rainy weather the DC area has been having, it should be easy to pluck them out of the ground. Do it now before they set seeds...which will just make weeding a bigger chore next year!