Law’s Brigade served as a member of Hood’s Division in the First Corps, Army of Northern Virginia. The unit, comprised of five Alabama infantry units, was commanded by Brigadier General Evander McIvor Law (August 7, 1836 – October 31, 1920). Law was an author, teacher, and a Confederate general in the American Civil War.
The marker, also known as the Law's CS Brigade Advance Tablet, is located on the southern most part of Warren Avenue, on the right or southwest side of the road if traveling southeast, opposite the south slope of Little Round Top. 
The tablet faces northeast. The tablet is a few feet away from the road and 158 feet from the intersection of South Confederate/ Wright/ Sykes Avenue. The four way intersection has four different names. This immediate location is completely overrun with monuments. The tablet is located very close to the road so there is no walking down the boulder-strewn hill to get at it. These monuments were first built in 1900 and concluded in 1906 according to the NRHP nomination form. One site has the monument being erected in 1910. It is amazing with all the work and effort exerted to make the Gettysburg National Military Park a reality, no one took the time to keep accurate records and correct installation dates. The work was done under the direction of the Gettysburg National Military Park Commission. The inscription on this tablet reads:
Army of Northern Virginia
Longstreet's Corps Hood's Division
Law's Brigade
4th. 15th. 44th. 47th. 48th. Alabama InfantryJuly 2 Arrived on the Field about 4 p.m. and advanced against the Union positions. The 4th, 15th, and 47th Regiments attacked Little Round Top and continued assault until dark. The 44th and 48th assisted in capturing the Devil's Den and 3 guns of Smith's 4th New York Battery.
There are scores of similar monuments for the various Confederate States & Union units which fought at Gettysburg. Four designs represent brigade, division, corps and army headquarters, and each has elements which identify it as Union or Confederate. Many of the tablets were created by Albert Russell & Sons Co. of Newburyport, Massachusetts and are made of granite, bronze and concrete. All of these tablets were designed by architect E.B. Cope. He designed pretty much every tablet for both the Union and Confederate armies, each one distinct, with several different varieties. The monuments were erected just after the turn of the century during the first and beginning of the second decade of the 20th century. Everyone has since been preserved or restored at least twice since the turn of the 21st century. The plaques and tablets were erected by the War Department and then, in later years, by the Gettysburg Battlefield Commission.
On October 1, 1898, the Gettysburg National Military Park Commission in a letter to the Secretary of War set gave recommendations for continuing the task of organizing and progressing the work of the Gettysburg National Military Park. The following is an excerpt from that report relevant to this waymark. The link at the end of the paragraph will take you to the entire report.The method of marking the positions of troops on this field, as approved by the War Department, is to place the principal tablet or monument of each command at the position occupied by the command in the main line of battle, and to mark the several important positions subsequently reached by each command in the course of the battle by subordinate and ancillary tablets, with appropriate brief inscriptions giving interesting details and occurrences and noting the day and hour as nearly as possible. SOURCE
Information about these specific types of monuments:
CONFEDERATE BATTERY AND BRIGADE TABLETS (ADVANCED POSITION)
These tablets are 3’8" x 3’4" in dimensions, with carefully prepared inscriptions cast in raised letters painted in white (contrasting the black background) describing the part taken in the battle by each brigade, their position and stating its numbers and losses so far as practicable to obtain. They are mounted on iron pillars or fluted cast iron posts about 3 feet high, grouted in the ground, and the tablets are inclined at a suitable angle so that the inscriptions can easily be read by persons riding or driving on the avenue. Every tablet is 4’4" in height. The advance position markers were cast by Calvin Gilbert. SOURCE & SOURCE
The Law's Brigade - CS Advance Position Marker is a contributing feature to the Gettysburg National Military Park Historic District which is nationally significant under NR Criteria A, B, C & D. Areas of Significance: Military, Politics/Government, Landscape Architecture, Conservation, Archeology-Historic. Period of Significance: 1863-1938. The original National Register Nomination was approved by the Keeper March 19, 1975. An update to this nomination was approved by the Keeper on January 23, 2004. The monument is identified as structure number MN551.
From the Nomination Form:
1 of 100 Civil War tablets in the park locating the positions of batteries and brigades not otherwise marked by monumentation. Mark's position of Law's CS Brigade Advance on July 2, 1863. Narrates events associated w/ Brigade during Battle.
Short Physical Description:
Cast iron tablet, 3'8" x 3'4", with raised inscription painted in a contrasting color and mounted on fluted cast iron post. All 4'4" H. Cast by Calvin Gilbert.
Long Physical Description:
Located on S side of Warren Ave, opposite south slope of Little Round Top.
My Sources
1.
NRHP Nomination Form
2.
Stone Sentinels
3.
Virtual Gettysburg
4.
Draw the Sword
5.
Historical Marker Database