The last sign of resistance (5)
I believe the answer is:
omega
This clue might be a double definition.
'the last' is the first definition.
(I've seen this before)
'sign of resistance' is the second definition.
'omega' can be an answer for 'sign' (omega is a kind of sign). I am unsure of the 'of resistance' bit.
Can you help me to learn more?
(Other definitions for omega that I've seen before include "Conclusion" , "Last letter of the Greek alphabet" , "character from Athens" , "Greek character symbolizing resistance" , "character in Greek literature?" .)