It's said to be a sign of something boring (5)
I believe the answer is:
auger
'something boring' is the definition.
(I've seen this before)
'it's said to be a sign of' is the wordplay.
'it's said' shows a homophone (sound like).
'to be' becomes 'owe' (owing is a kind of being).
'a sign of' becomes 'ger' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'owe' sounds like 'au'.
'au'+'ger'='AUGER'
Can you help me to learn more?
(Other definitions for auger that I've seen before include "A tool for boring hole in wood" , "Tool for boring holes in wood" , "I bore" , "Tool with spiral point for boring" , "Boring instrument" .)