: This is typically a manufacturer's internal code or a UL file "mark" indicating the factory that fabricated the raw PCB.
: For general properties of boards with this rating, you can refer to the UL 94 flammability standard which defines their thermal and safety limits. sh1 94v0 datasheet free
If the component is a black, square plastic box (about the size of a sugar cube) with 4 or 5 pins, it is likely a . : This is typically a manufacturer's internal code
If you are reviewing the quality of a PCB marked with 94V0: sh1 94v0 datasheet free
: This is a UL 94 flammability standard rating from Underwriters Laboratories (UL). It indicates that the PCB material is self-extinguishing within 10 seconds of a flame being removed.