Eureka!

Markers are two or more soldiers usually from the battalion pioneers (engineers) detailed to stand where ever placed to set the initial alignment of the battalion's formation or to indicate the direction of march or turning points for a column in march.
http://www.publiusforum.com/ig/generalguides.html

........

http://history.farmersboys.com/Amalgamation/Amalgamation%20parade%20RGBW.htm

See Photo under Parade Memories, "Marker take up position at Windsor

........

Also 62d N.Y.S.V.V. Flank Marker Flag at:
http://andersonzouaves.tripod.com/livinghistory/