This plate features the Type 2 layout with "SC" straight across - this is more rare than the "stairstep" S/C layout. Having seen the color picture on the original listing back in 2005, the quality of the one shown here is exceptional with no nicks/scratches in the paint, all original condition, not repainted, and presumably unused.
Typically, 'stairstep' 1917 plates are the most common, and rarely exceed $1,200-$1,500; less depending on quality. With the less common 'straight' SC shown here, apparently two deep-pocket collectors went to battle to run this listing over $9K. Depending on condition, $2,500 would typically be the maximum to be expected.