The 90th PA monument is shaped like a tree trunk with all the limbs shot off. Near the top is a bird’s nest. During the battle the limbs were shot off the tree and the nest, containing baby birds, fell to the ground. One member of the 90th laid down his rifle and placed the nest back in the tree.

See http://www.virtualantietam.com/vgExhibit/monuments/detail.php?curMon=sr347

Another monument that fascinates me is dedicated to a regiment that fought near one of the barns in Gettysburg. It shows horse flies and hornets flying around the soldiers and horses.

And there are monuments at Gettysburg that are historically incorrect. For example, the rifle held by the trooper on the 17th PA Cavalry monument is a Spencer carbine, but the regiment wasn't armed with those until 1864. At Gettysburg they carried Sharps single-shot breechloaders

The 155th PA monument on Little Round Top presents a soldier of the regiment in a Zouave uniform. At the time of the battle the 155th still wore the standard Union uniform; they did start wearing the distinctive Zouave uniform until 1864.