It wasn't until 1932 that a permit was required to carry a concealed weapon in the District of Columbia. It was legal to carry pistols openly until 1943. At the time, it was clear that the prohibition on open carry did not apply to long arms.
In 1973 the District of Columbia was granted "home rule". In 1976, the new District government passed the Firearms Control Regulations Act of 1975. The law went into effect in 1977. It has been over 70 years since it was legal to openly carry a pistol in the District of Columbia.
In the recent court decision on Palmer v. D.C., judge Scully relies heavily on the Peruta decision in the Ninth Circuit, saying it is clear that their exists a constitutional right to carry guns outside the home, and that the existing bans on the general carry of guns outside the home are unconstitutional. Peruta strikes down the local discretion to deny carry permits to the vast majority of applicants.
The D.C. Police Chief has ordered the police force not to arrest people carrying pistols unless they have felony records. One unknown second amendment activist has taken the opportunity to obtain a photograph of himself openly carrying in the District.
He will likely be the first of many.
D.C. attorneys have requested a stay for 180 days. Here is a link to the request.
Link to Gun Watch