It means something when you put your name to a letter (6)
I believe the answer is:
signal
'it means something when you put your' is the definition.
The definition suggests a singular noun which matches the answer.
'name to a letter' is the wordplay.
'name' becomes 'sign' (I can't justify this - if you can you should give a lot more credence to this answer).
'to' means one lot of letters go next to another.
'letter' becomes 'l'.
'sign'+'a'+'l'='SIGNAL'
Can you help me to learn more?
(Other definitions for signal that I've seen before include "Gesture; notable" , "Communication by sign" , "Outstanding - information sent over a distance" , "See 7" , "Notable; warning sign" .)