Just a few to be going on with . . . .
AB = Absolute Block
ABCL = Automatic Barrier Crossing Locally Monitored
AHBC = Automatic Half Barrier Crossing
AOCL = Automatic Open Crossing, locally monitored
AOCR = Automatic Open Crossing, remotely monitored
AOM = Area Operations Manager
APT = Advanced Passenger Train
ARM = Asset Recovery Manager
ARS = Automatic Route Setting
ASC = Area Signalling Centre
AWS = Automatic Warning System (see TPWS)
CAPE = Train will not run. Cancelled from origin,
C&W = Carriage and Wagon
CET = Controlled Emission Toilet
COA = Change Of Aspect
COSS = Controller of site safety
CWR = Continuous Welded Rail
DRA = Drivers Reminder Appliance
DSD = Driver's Safety Device
DVD = Driver's Vigilance Device (Sometimes referred to as the VIG)
ECS = Empty Coaching Stock
ERTMS = European Rail Traffic Management System
ES = Engineering Supervisor
ELR = Engineers Line Reference
EPS = Enhanced Permitted Speed (used for tilt-enabled Class 390s)
EROS = Emergency Restriction of Speed
ESR = Emergency Speed Restriction (dont know what the difference is betteen these two)
FPL = Facing point lock (also EFPL economic facing point lock)
HABD = Hot Axle Box Detector
HOBC = High Output Ballast Cleaner
HPSS = High Performance Switch System
HSM = Hand Signalman
IBJ = Insulated Block Joint
IWA = Individual Working Alone
LUL = London Undergound Lines (?)
LWR = Long Welded Rail
MAS = Multiple Aspect Signal (usually colour light as opposed to semaphore)
MC = Machine Controller
MCB = Miniature Circuit Breaker
MCB = Manually Controlled Crossing with barriers
MSP = Measured Shovel Packing
NMT = New Measurement Train
NR = Network Rail
LXA = Level Crossing Attendant
MOM = Mobile Operations Manager
OHL or OHLE = Overhead Line (Equipment)
OTM = on track machine
OTMR = On Train Monitoring Recorder (the "spy in the cab")
OSS = Overspeed Sensor System
PICOP = Person In Charge Of Possession
PINE = Train will be terminated short of destination
PLB = possession limit board
PoSA = Proceed on sight authority
PSB = Power Signal Box
PSR = Permanent Speed Restriction
PW = Permanent Way
RA = Right away
RCF = Rolling contact fatigue
RETB = Radio Electronic Tken Block
RIO = Rail Incident Officer
RPI = Revenue Protection Inspector
RRAP = Road Rail Access Point
RRV = Road/Rail Vehicle
RSF = Right Side Failure
S&C = Switches and Crossings
S&T = Signls and Telelecomms (also Sick and Tired

)
SCC = Signalling Control Centre
SIMBIDS = Simplified bi-directional signalling
SLU = Standard length unit (for calculating goods train lengths for loops etc.)
SPAD = Signal passed at danger (also SASPAD = Start against signal and passed at danger and SOYSPAD = Starting On Yellow Signal Passed At Danger)
SPATE = Speed Previously Advised Terminated Early
SPRS = Signal Post Replacement Switch
SPT = Signal Post Telephone
SSI = solid state interlocking
STP = Short term plan (a train working at short notice) see also VSTP
TBW = Temporaary Block Working
TCB = Track Circuit Block
TCF = Track Circuit Failure
TDM = Time Division Multiplex
TMD = Traction Maintenance Depot
TOPS = Total Operations Processing System
TPWS = Train Protection & Warning System (see also AWS)
TRTS = Train Ready To Start
TRSMD = Traction and Rolling Stock Maintenance Depot
TRUST = Train Running System TOPS
TSR = Temporary Speed Restriction
TSS = Train Stop System (on LUL)
UFN = Until further notice
UFN = Unpaid Fare Notice
UWC = User-worked Crossing
VSTP = Very Short Term Plan (see also STP)
WILD = Wheel impact load detector (also WHEELCHEX = Lineside detector for wheel flats)
WSF = Wrong Side Failure
WSP = Wheel slide protection