Greetings Hi Mr. Turchin:
As far as we know, the heiograph proper was not introduced into military operations until after the War of 1861. Since these forums are generally International in scope I and judging that you are refering to the American Civil War.
The Signal Corps Association (1860-1865) at: www.civilwarsignals.org has knowledge that both Federal and Confederate army signal corpsmen were experimenting with mirrors as wel as more expensive electric and carbon arch lights.
There is an 1863 account where a Lieut. E. A. Denicke conducted experiments with mirrors both at Rockville, Maryland and again at New Orleans, Louisiana.
confederates were known to have used mirrors upon Massanutten Mountain in Virginia's Valley.
Hope this helps a bit.
Signal Corps Association Re-enactors' Division (SCARD)