They were painted that way to advertise a B&O customer service.
The special paint job was initially done by the builder, ACF.
Yes. they were used in LCL service at times, but not dedicated to it like NY Central's "Pacemaker" cars of the same period.
These paint jobs were no longer maintained after 1953 (?) but it could be seen much later on any such car that was in good condition and had not been in an accident.
Repaints were B&O oxide red, sometimes with a white Sentinel slogan.
The rarer orange comet "Time Saver" box cars, of which only 7 or so have been counted in photos, were also advertising specials.
They seem to have been randomly done and often first seen at state fairs in B&O territory.
This paint job disappeared quickly, with repaints done in oxide red and a white Time Saver stencil, which like the Sentinel Service stencil, was used on other box cars as well.
In B&O service, any box car that was clean, tight and in good condition was used for LCL service.