Postcards are cataloged in the Photo catalog.
The General Postcard Collection follows an in-house subject-based cataloging scheme. Object IDs begin with PC, then a 2-letter code that indicates the general subject, then a period followed by a letter relating to the specific location depicted in the postcard.
The object ID for this postcard, for example, is PC HO .CapH: It's a postcard showing a drawing of the Capitol Hill Hotel on the south side of the 100 block of C Street NE.
In addition to the General Postcard Collection, see: