Sign in East Street with one copper left in crowd (11)
I believe the answer is:
gesticulate
'sign in east street' is the definition.
'gesticulate' can be an answer for 'sign' (I've seen this before). I am unsure of the 'in east street' bit.
'with one copper left in crowd' is the wordplay.
'with' is an insertion indicator.
'one' becomes 'i' (Roman numeral).
'copper' becomes 'cu' (Cu is the chemical symbol for copper).
'left' becomes 'l' (common abbreviation).
'in crowd' becomes 'gestate' (I can't explain this - if you can you should give a lot more credence to this answer).
'i'+'cu'+'l'='icul'
'icul' put into 'gestate' is 'GESTICULATE'.
Can you help me to learn more?
(Other definitions for gesticulate that I've seen before include "Express by movement rather than words" , "Express oneself by hand movements, etc" , "Sign" , "Make vigorous hand movements" , "Wave" .)