A siren can show him points
I believe the answer is:
sir
'a siren can show him points' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'him points' is the wordplay.
'him' becomes 'Si'.
'points' becomes 'r' (I can't explain this - if you can you should give a lot more credence to this answer).
'si'+'r'='SIR'
Can you help me to learn more?
(Other definitions for sir that I've seen before include "Term of address for a gentleman" , "Gentleman's form of address" , "Title for knight or teacher" , "Honourable title" , "Title of 1 across" .)