What do this casting mark mean ?

[Racer57]

I've seen this a lot and have always wondered what it meant.  Anyone know ?

[Skdmark]

Hour of manufacture.
Some castings also have a pointer with a D and N for dayshift or nightshift.

[Racer57]

Ok that makes sense. So if there is a bad batch, they know who to blame.   

[HP_Cuda]

Gee I wonder if there were more problems on a Friday afternoon....