Warning of danger shown by revolutionaries (3,4)
I believe the answer is:
red flag
This clue might be a double definition.
'warning' is the first definition.
(I've seen this before)
'danger shown by revolutionaries' is the second definition.
I know that 'danger' relates to this answer.
'of' is the link.
Can you help me to learn more?
(Other definitions for red flag that I've seen before include "A number of revolutionaries" , "signal to stop" , "Instruction to halt" , "A flyer" , "Socialist anthem" .)