Henderson - Stamps
Makers were not always consistent in stamping their bagpipes. Some didn't at all. I asked Jack Dunbar about this at one point in time. He rummaged in his desk and tossed these two tools in front of me. These were held vertically atop the piece to be stamped. Using your chin, you put as much weight as you could muster onto the tools and rocked the piece back and forth until the stamps left its impression. My neck hurts just thinking about this. They hated the job at the Henderson shop and sent as many bagpipes as possible out without a stamp.
A number of stamps can be found on Henderson bagpipes. They are generally found either between the cord beads (holders) or directly below them. There is one example here of the stamp being set on the cord bead. I've only seen this once. Efforts have been made to establish approximate dates of use. It is generally accepted that "P. Henderson Glasgow" is probably the earliest stamp however there are no guarantees to that.

You may find
Henderson
P.Henderson
P. Henderson
P. Henderson Glasgow
P. Henderson Ltd.