This appeared today in "DCWatch":

Boundary Markers
David Sobelsohn, dsobelso-at-capaccess-dot-org

In last Wednesday's issue of themail, John Cleave asked about a DC/MD
boundary marker at Wisconsin and Western Avenues, NW. Tellingly, he
thinks the marker went up before 1928, perhaps much earlier. My sense
is that, unlike most states, DC has few markers, even on major roads,
to indicate that a motorist is entering the District (let alone signs
saying "Welcome to Washington"). A striking example is where US-50
crosses the Baltimore-Washington Parkway, US-50 becoming New York
Avenue and the BWP becoming Kenilworth Avenue. The sign for New York
Ave. says "To Washington." The sign for Kenilworth Ave. says "To
Richmond" even though a driver taking either route will enter DC at
pretty much the same time, and even though a driver taking the
Kenilworth Ave. route will go clear across both SE and SW DC before
getting to Virginia (let alone Richmond). Neither route actually has a
sign indicating that the car has entered DC. I had to study a map
before realizing that taking Kenilworth Ave. would also get me into
DC. So my questions to themail subscribers are: where else, besides
Wisconsin and Western Avenues, NW, are there actual boundary markers
at the DC/MD border; are any of recent vintage; and are any visible to
motorists?

Another, perhaps more troubling question: why does the sign on a road
going into SE and SW DC say "To Richmond" but not "To Washington"?