D.C. Code § 10-503.14
It is forbidden to offer or expose any article for sale in said United States Capitol Grounds; to display any sign, placard, or other form of advertisement therein; to solicit fares, alms, subscriptions, or contributions therein.
July 31, 1946, 60 Stat. 718, ch. 707, § 4
1973 Ed., § 9-121.
1981 Ed., § 9-110.
This section is referenced in § 10-503.18.