The 36 CFR 7.96 discussion in Federal Register / Vol. 50. No. 161 / Tuesday, August 20, 1985 /33571 shows that the rules regarding signs are for "signs and placards" that have the capacity to be unattended, not the signs that demonstrators normally hand-carry. This is a substantial change in my understanding of the regulation, but makes sense in the historical context, linked to above, and in the wording of the regulation itself: 1) signs and placards, and 2) the sizes contemplated, which are large.
"The National Park Service is not proposing to prohibit demonstrations in Lafayette Park. Nor is it proposing to place any limitation on signs that are hand-carried. The Park Service is merely proposing to place reasonable, content-neutral limitations on signs placed down in Lafayette Park so that visitors might be able to enjoy the history and beauty of the Park while demonstrators continue to have ample avenues of communication. In addition, the proposed rule would apply only to Lafayette Park and not to the many other park areas in close proximity, for example, the Ellipse on the south side of the White House."