Hmm. That's kinda difficult!
Space Police Usomething Division, comes to mind, but I have no clue what the U could/would be.
Following along on Manere's train of thought... ummm, maybe Space Police United Defence? Or something like that?
I don't know if this will work figuring how the DOTROTPOTUSF is abbreviated, but how about this? Space Patrol Unit of the DOT ROT POT USF.
I know nobody reads this anymore, but I think the game actually does say what the first two letters stand for. It's when the gang is asked to find the baki spud. When the Spud appears, they say
"Ranger Knox here of the Space Police... umm... S.P.U.D..."
So I guess it's Space Police U? D?.... But what do the U and D stand for? I guess we'll never know for sure.
Hey! I wasn't too far off with my guess then!