This lovely photograph is online in the MOLLUS Massachusetts Collection (Vol. 40, pg. 1994) at the US Army Heritage & Education Center. It was listed in the catalog for Photographic Incidents of the War; from the gallery of Alexander Gardner, photographer to the Army of the Potomac (1863) as having been taken in November 1863, though the MOLLUS mat notes say October.

It was also published in F.T. Miller’s Photographic History of the Civil War (Vol. 8, pg. 327; 1911), which is where these men are identified:

Standing, left to right, Lt. Frederick E. Beardslee, Lt. William H.R. Neel, Lt. George J. Clarke, [unknown], Capt. Charles L Davis;
Seated, left to right: Lt. Charles J. Clarke, Lt. William S Stryker, and Lt. Adin B. Capron.

From their pictures in Brown’s The Signal Corps, U.S.A. in the War of the Rebellion (1896), I think the man seated at left is Thomas R Clarke, not Charles; Charles was wounded at Fredericksburg in December 1862 and discharged in March 1863. And the “unknown” officer may be Capt. Robert Patterson Hughes, much later Major General, USA.

Here are Clarke and Hughes from Brown:

Other sources have the man seated on the box as Lt Fountain Wilson rather than Stryker, and I agree. From Brown, again:

Of this group of 8 signal officers, two, Lieutenants George J Clarke and Fountain Wilson were on the Maryland Campaign of 1862; Lt Clarke was one of several signal officers and men on the battlefield of Antietam under fire on 17 September 1862.

Although probably not pictured with this group, Lieutenant William S. Stryker was also at Antietam.

After his service in 1861 as First Sergeant of Company C, Duree’s Zouaves, pictured here, Norman Henry Camp was commissioned a Lieutenant in the 4th New Jersey Infantry. He was on detail to the Signal Corps at Antietam in September 1862.

This photograph is online from the US Army Heritage & Education Center [CWP 189.66].

This Brady Studio portrait of Captain Joseph H Spencer was probably taken soon after he was commissioned Captain in the Signal Corps and assigned to the Office of the Signal Officer of the Army in Washington, in April 1863. He been a signal officer since being detailed from the First Minnesota Infantry in August 1861, and was on the Peninsular and Maryland Campaigns.

The original print is online from the Library of Congress.