Serving up potato on time, showing sign of distress (6)
I believe the answer is:
mayday
'sign of distress' is the definition.
'Mayday' can be an answer for 'sign' (Mayday is an example). I'm not certain of the 'of distress' bit.
'serving up potato on time' is the wordplay.
'serving up' says the letters should be written backwards.
'potato' becomes 'yam' (I have seen 'Sweet potato' mean 'yam' so perhaps 'potato' could also mean 'yam').
'on' means one lot of letters go next to another.
'time' becomes 'day' (day is a kind of time).
'yam' back-to-front is 'may'.
'may'+'day'='MAYDAY'
'showing' is the link.
Can you help me to learn more?
(Other definitions for mayday that I've seen before include "Radio distress call" , "International radio distress signal" , "Request for help" , "call for help?" , "I'm in trouble" .)