Nelson Moyer wrote:
The loading prohibitions on the stencil under discussion are one of several stencils used by the CB&Q. Kit decals may or may not include these stencils, but they can easily be fund in a decal set offered by Jerry Hamsmith. Jerry’s set includes ‘Return Empty to …’ and For … Loading Only’ stencils, plus several other special instructions.
I once asked a former car clerk, whether those kinds of car-side restrictions or "return to" legends were observed. "Sure," he said, "when it was convenient."