Duke Nukem 3D Addon Map Credits

Duke It Out in D.C. Map Credits

Hell to the Chief - Robert Travis
Memorial Service - Robert Travis
Nuked Files - Robert Travis
Smithsonian Terror - Robert Travis
Capitol Punishment - Robert Travis
Metro Mayhem - Robert Travis
Brown Water - Shawn Swift
Dread October - Robert Travis (Has a truck copied from Final Destination)
Nuke Proof - Robert Travis
Top Secret - Charlie Wiederhold

Duke Caribbean Map Credits

Caribbean Catastrophe - Robert Travis
Market Melee - Charlie Wiederhold
Mr. Splashy's - Robert Travis
The Wavemistress - Charlie Wiederhold
Lost Lagoon - Robert Travis
Voodoo Caves - Tyler Larsen
The Alien Remains - Charlie Wiederhold
A Full House - Bill Buchalter (with final changes by Robert Travis)
Island Hopping - Charlie Wiederhold
Hidden Grotto - Charlie Wiederhold
Cruiseship - Charlie Wiederhold
The Docks - Charlie Wiederhold (not tagged in-game but confirmed on Duke4 forum)

Credits lists Bill Buchalter, Tyler Larson, Shawn Swift (Shawn confirmed in an email that he did not work on the addon)

Nuclear Winter Map Credits

Deja Vu - ??? / Still has Allen H. Blum III's signature
Where It All Began - ??? / Still has Allen H. Blum III's signature
Land of Forgotten Toys - ???
Santa's Corporate HQ - ???
The Backdoor - ???
Christmas Village - ???
Here Comes Santa Claws - Michael Clark
Santamatch - ???
Credits lists Scott Haslam (Dagger), Krystian Palys, Michael Clark (CombatAnt)

Duke Xtreme

The Convention - ???
Crash - ???
Dim Park - ???
Dirge - Robert Travis
Exanagon - Robert Travis
Final Destination - Shawn Swift
Frankenstein - Shawn Swift
Garage - ???
Garbage - ???
Helicopter - ???
Hoth - Robert Travis
MIR Attrition - Shawn Swift
Missile Silo - ???
Monoliths - ???
Munitions Dump - Shawn Swift
Opaka - Robert Travis
Pestilence - Shawn Swift
The Rift - Shawn Swift
Rigel - Robert Travis
Rimshots - ???
Sanitation Plant - ???
Shakaar - Robert Travis
Studio 9 - "PJA"
Toys - ???
YDTC - "PJA"
6 Spires - Robert Travis
AnslemX - Robert Travis
BJEDM - ???
Con-Am - Robert Travis
Convenience Store Feud  - ???
Dark Blume - ???
Disco Duke - ???
Duckhunt - ???
End To End - "NLB"
Eye of Ra - ???
Game Show - ???
Ice Flow - Robert Travis
Mini-Doom - Robert Travis
Mohave - Robert Travis
Old House - Robert Travis
On High - Robert Travis
Pac-Rat - ???
Red Orbit - Robert Travis
Rhombico - ???
Rigamarole - ???
Steel Maze - ???
Teseract - ???
The Maze - Robert Travis
Under Ice - ???

Duke!Zone
http://pastebin.com/GPNmNu60
Duke!Zone 2
Alan Smithee

Signatures

Robert Travis - Either RT or RT and a star near it
Charlie Wiederhold - Wieder or a stylised CS
Shawn Swift - SCS (sometimes followed by a smiley face)
Tyler Larsen - Bliss written inside the map
Michael Clark - Combatant (CombatAnt) written largely

Credits of Credits List
Charlie Wiederhold for confirming a few levels
Methy for their in depth research comparing mapping styles