PID stands for Packet Identifier. The SCTE 35 PID entry is shown only if SCTE 104 AD Insertion Triggers are enabled.

SCTE-35 Example Source Code

The only Apple supported way of including SCTE-35 data is via the EXT-X-DATERANGE tag with the various SCTE35 attributes.

See the spec for the details -

See also the WWDC 2016 video - What's New in HTTP Live Streaming - which talks about the various ways metadata can be included in HLS streams.