The sign indicates a marker for The Arlington Line.
The sign notes a historical fact.
Not all signs are there to show a historical fact.
exists e1 x1 x2 x3 x4.(ne_org_line(x3) & (x3 = x4) & ne_org_arlington(x4) & n_sign(x1) & Theme(e1,x2) & Actor(e1,x1) & v_indicate(e1) & for(x2,x3) & n_marker(x2))
exists x2 x3.(n_note(x2) & of(x2,x3) & n_sign(x3) & all s1 x1.((n_fact(x1) & a_historical(s1) & Theme(s1,x1)) -> (a_topic(x2) & for(x2,x1))))