Some believe the hands are flashing sign language.
"French used Lincoln's life mask as well as casts of Lincoln's own hands as models."
http://www.yeodoug.com/resources/dc_french/lincoln_memorial/dcfrench_lincoln_memorial.html
"Another popular legend is that Lincoln is shown using sign language to represent his initials, with his left hand shaped to form an "A" and his right hand to form an "L". The National Park Service denies both stories,... Gerald Prokopowicz writes that, while it is not clear that sculptor Daniel Chester French intended Lincoln's hands to be formed into sign language versions of his initials,...he would have had a reason to do so, i.e., to pay tribute to Lincoln for having signed the federal legislation giving Gallaudet University, a university for the deaf, the authority to grant college degrees. The National Geographic Society's publication, 'Pinpointing the Past in Washington, D.C.' states that Daniel Chester French had a son who was deaf and the sculptor was familiar with sign language."
https://en.wikipedia.org/wiki/Lincoln_Memorial
Is it really sign language?
"Not really, but that doesn't stop people from wondering. The sculptor Daniel Chester French intended to show Lincoln's "physical and mental strength" and his "confidence" through the sculpture's posture and features. Lincoln's left hand is clenched, while his right hand curled around the end of the armrest, his index finger slightly lifted from the chair. The fist echos themes of strength and power found elsewhere in the memorial as
fasces"
http://www.nps.gov/linc/faqs.htm
