Elgin Grade 288

This is an Elgin grade 288, 18 size, 7 jewels, made about 1908. 

Here are some images showing the secondary serial number markings on the base plate, dial side, and the under side of the balance cock.

These secondary stamps are often prefixed with a symbol standing in for the first few digits. I suspect this system had something to do with how inventory and production runs were organized, but the exact reason is lost to time.

This watch has a one, with three lines above. The serial number begins with 13, so this makes sense.