D.C. Mun. Regs. tit. 3, r. 3-803
Overvotes or otherwise improper votes shall be deemed invalid and not counted. Improper votes shall include, but are not limited to, votes which the voter is not lawfully able to cast.
Any overvote or otherwise improper vote in one (1) or more contests shall not invalidate the entire ballot but only the votes cast in that contest. All correctly cast votes on such a ballot shall be counted. The number of votes rejected because of overvote or otherwise improper vote shall be reported.
An undervote shall not invalidate the entire ballot, except that a ballot cast without any marks shall not be tallied. If a voter fails to mark a choice for a contest or ballot question, only those contests and questions that were unmarked shall not be counted.
A write-in vote shall not be adjudged valid, and shall not be tallied and recorded, unless the voter has written, or used a stamp to imprint, the name of the write-in candidate on a blank line provided for write-in voting and has not marked the voting position on an equal number of votes allowed for that office. Any write-in vote cast using a sticker or adhesive label shall be invalid.
When a voter writes a person's name in the proper space for write-ins for an office, it is a vote for that person, notwithstanding:
In the case of a write-in vote, no ballot should be regarded as defective due to unclear writing, misspelling of a candidate's name, or by abbreviation, addition, omission or use of a wrong initial in the name, so long as voter intent can be determined.
If a voter circles a candidate's name, draws an arrow pointing to a candidate's name, circles the empty oval to the left of the candidate's name, uses a check, asterisk, or any other mark in a manner that clearly indicates his or her intended choice, the vote shall count as a vote for that candidate, provided, that the mark is not a distinguishing mark as defined in § 803.9.
A ballot properly marked by filling in the empty oval to the left of the candidate or ballot question is valid even though it contains an additional mark, provided that the additional mark is not a distinguishing mark as defined in § 803.9.
A distinguishing mark is a mark (whether a letter, figure, or character) that serves to separate and distinguish a particular ballot from other ballots cast at the election. The mark itself shall be to furnish evidence of an unlawful intention on the part of the voter to identify the ballot after the vote has been cast, such as the voter's initials, or a mark known to belong to the voter.
D.C. Mun. Regs. tit. 3, r. 3-803