In response to my inquiry concerning the Wray collection having a CS First National from CS signal station at Battery Gregg, Charleston harbor, I received the fol response from NPS historian Rick Hatcher in Charleston:
"To my knowledge CS Signal Corps detachments in the Charleston area did not
carry first national CS garrison flags (or any other CS flag) as part of
their supplies and/or materials. However, a garrison flag being flown at
Battery Gregg on a daily basis is logical. Some CS invoices for CS forces
in Charleston in 1861 included 10 ft x 15 ft. 1st Nationals being made by
local vendors. So it is more likely this flag was Battery Gregg's flag and
not a flag carried by Signal Corps.

"Also of note, as the 2nd National CS flag was adopted in May 1863, its
interesting that a 1st National was still in use two months later. However,
some units continued to carry 1st Nationals after May 1863, and the same
could be true at Battery Gregg."

[This accords with my own supposition, that the flag did not represent the colors of the signal station itself, but that of the installation being served.]