Crystal-Gemmed Signet: Riftseekers' Sanctum
"Obtained from a Dragorn in Riftbreakers Sanctum" (A Dragorn Battlemaster - PH is in Taromani's room itself)

Discolored Signet: Sewers of Dranik
"Obtained from a Dragorn in the Sewers of Dranik" (Map C - far SE room - a cunning dragorn - PH is a twisted stoneworker)

To get expedition say: "Sewers" to Grand Historian Rygua and he must reply:
'You have chosen to explore the Sewers of Dranik. Beware during your travels there should you come across a dragorn known as the Dragorn Foreman, or an ukun known as the Ukun Sentinel..."

If he says this you have the right instance, zone in and move to spot. Either have one trigger the traps (they make you loose invis) or clear at the traps. If the normal not-seeinvis change to undeads (can kill one roamer there and change to ivu) - move to campspot and clear the PHer. Only PHer/Named and one undead roamer move to camp.

Dust-Marred Signet - Catacombs of Dranik
"Obtained from a Dragorn in the Catacombs of Dranik" (Insidious dragorn - PH is a noc scout)

Position one of the groupmembers at the Historian to get the missions. If you say "catacombs" and he mentions "Master of the Watch", you've got the right one. Have a tracker zone in and check for insidious dragorn - if not up leave mission again and reget it until the named is up from the start. Saves a lot of time altho the mission-getting sucks.

Inside you have a see invis rat as well as a bat that will aggro if you kill the rat. Kill both, invis and move up to the next see invis rat and setup camp there if you have a FD puller. Snare named and click invis and move back. Mobs on diff faction or light blue and you can pull named single far away. If not snared the guy moves into the room and aggro's 6+ mobs so if no fd-snare puller prolly better clear.

Glimmering Signet - Muramite Proving Grounds
"Obtained from a Dragorn in the Muramite Provingrounds" (A Dragorn Tactician lvl 73 1200 max, partially slow, AE = Dragornian Malady{ PB AE 50', Disease (-150) -200hp, 100hp DoT}, PH a dragorn sentinel, loc -3728, -601).

Several Spots again - one west of ODI, one east of ODI, one near TF/BH camp and I think one more. Get a tracker or if good dps clear 2-3 PHers from ODI.

Tarnished Signet - Wall of Slaughter
"Obtained from a Dragorn in the Wall of Slaughter" (Dragorn Strategist, A Dragorn Mastermind - PH is a dragorn serf).

There is at least 6 spots where these can pop (near MPG ramp, anguish entrance x2, bit north of the portin, south of the porting, southwest of the portin). Just get a tracker and there should be one up.

Two-Toned Signet - Dranik's Hollows
"Obtained from a Dragorn in Dranik's Hollows" (A Shrewd Dragorn - lvl 70, 843 max, partially slow, PH = a blighted cave rat)

Spam the Grand Historian in Dranic Scar until you get "Watering Hole" as expedition. Leave and reget as long as you get this one, as the signet only drops there !
Inside the position of the PH/Named is visible HERE.

Weather-Worn Signet - Ruined City of Dranik
"Obtained from a Dragorn in the Ruined City of Dranik" (A Dragorn Prodigy, spawn location is just before the bridge with lirah the bridgekeeper (near location 7 on map below) - PH is a dragorn turncoat)

There is some more spawnpoints, if you have a tracker its worthwile to check if the prodigy is up elsewhere. One spot is in the tunnels north of Krekk Brimblade, one spot is a bit south of Battlemaster and the most known one is indeed south of the bridgekeeper.