Notice a bit of a rash (4)
I believe the answer is:
spot
'notice' is the definition.
(spot can mean to notice or observe)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for spot that I've seen before include "20 [MARK]" , "Notice - place" , "Notice; skin blemish" , "Lady Macbeth: ''Out, damned . . . .!''" , "jam > stain" .)