George,
It is 26850, built as a part of 26000-26999 by ACF in 1913. There were similar (identical?) cars built by ACF in 1911-12 in the 25000-25999 series. The paint scheme is interesting for the two series since it seems to mark the time when freight car lettering changed. 26850 wears its as-delivered scheme, or a replacement since there is no builders stencil. This seems to be the time when this scheme was introduced, since the boxcars of the time had the same scheme. The previous cars in the 25000 series had the large block style "MONON" on the sides...which seems to have lasted only of few years. Some steam engines, like the H6 consols built in 1911, were delivered with it as well. Before this, although I can't put a date to it, there was the spelled out "Chicago Indianapolis & Louisvile" with "Monon Route" in an elaborate losenge herald. See attached for examples.
Regards,
Mike